## Rendezvous with Cassidoo Solutions
Solutions to the interview question of the week from the [rendezvous with cassidoo newsletter](https://buttondown.email/cassidoo)
Solutions in the following languages:
- TypeScript
- Elixir
Inspired and forked from [jda0](https://gist.github.com/jda0/01070831825ed63efcd1f626653a16a3)/rwc
/**
* Sort an array of strings based on the number of distinct
* characters that occur in the word (followed by the
* length of the word).
*
* $ charNumSort([“Bananas”, “do”, “not”, “grow”, “in”, “Mississippi”])
* $ do in not Mississippi Bananas grow
*
*/
const charNumSort = (input: Array<string>) =>
input
.sort((first, second) => {
// use Set() to find unique char count
const compare = [...new Set(first)].length - [...new Set(second)].length;
return compare ? compare : second.length - first.length;
})
.join(" ");
console.log(charNumSort(["Bananas", "do", "not", "grow", "in", "Mississippi"]));
// https://codesandbox.io/s/modest-sanderson-wxs33?file=/src/index.ts/**
* Given an array of random integers, move all the zeros in the array to the end of the array.
* Try to keep this in O(n) time (or better)!
* Example:
* $ moveZeros([1, 2, 0, 1, 0, 0, 3, 6])
* $ [1, 2, 1, 3, 6, 0, 0, 0]
*/
const moveZeros = (arr: Array<number>) => {
let numberOfZeroes = 0;
const result = arr.reduce((agg, curr) => {
curr ? agg.push(curr) : numberOfZeroes++;
return agg;
}, [] as number[]);
return [...result, ...Array(numberOfZeroes).fill(0)];
};
console.log(moveZeros([1, 2, 0, 1, 0, 0, 3, 6]));
// https://codesandbox.io/s/misty-forest-pxdog?file=/src/index.ts/**
* Given a string s and a character c, return the number of occurrences of c in s.
* Example:
*
* $ numChars(‘oh heavens’, ‘h’)
* $ 2
*/
const numChars = (input: string, char: string) =>
/**
* yay regular expressions! global flag since we wanna count *all* instances
* return 0 in case of no matches
*/
(input.match(RegExp(char, "g")) || []).length;
console.log(numChars("oh heavens", "h"));
// https://codesandbox.io/s/mystifying-swirles-8h5it?file=/src/index.ts/**
* Given an array of numbers that represent stock prices (where each number is the price for
* a certain day), find 2 days when you should buy and sell your stock for the highest profit.
* Example:
*
* $ stockBuySell([110, 180, 260, 40, 310, 535, 695])
* $ “buy on day 4, sell on day 7”
*/
const stockBuySell = (prices: Array<number>) =>
`buy on day ${prices.indexOf(Math.min(...prices)) + 1}\
, sell on day ${prices.indexOf(Math.max(...prices)) + 1}`;
// A much faster (the earlier one is ~88% slower, https://jsbench.me/54keiiwuvy/1) way
const stockBuySellReduce = (prices: Array<number>) => {
const minMax = prices.reduce(
(agg, curr, index, arr) => {
if (curr < arr[agg.min]) agg.min = index;
else if (curr > arr[agg.max]) agg.max = index;
return agg;
},
{ min: 0, max: 0 }
);
return `buy on day ${minMax.min + 1}, sell on day ${minMax.max + 1}`;
};
console.log(stockBuySell([110, 180, 260, 40, 310, 535, 695]));
console.log(stockBuySellReduce([110, 180, 260, 40, 310, 535, 695]));
// https://codesandbox.io/s/sharp-jepsen-8npl1?file=/src/index.ts/**
* Given an array of people objects (where each person has a name
* and a number of pizza slices they’re hungry for) and a number
* for the number of slices that the pizza can be sliced into, return
* the number of pizzas you need to buy.
*
* $ arr = [{ name: Joe, num: 9 }, { name: Cami, num: 3 }, { name: Cassidy, num: 4 }]
* $ gimmePizza(arr, 8)
* $ 2 // 16 slices needed, pizzas can be sliced into 8 pieces, so 2 pizzas should be ordered
*/
type TPeopleSlicesMap = {
name: string;
num: number;
};
const gimmePizza = (arr: Array<TPeopleSlicesMap>, maxSlices: number) => {
const totalSlices = arr.reduce((total, { num }) => {
return (total += num);
}, 0);
return Math.ceil(totalSlices / maxSlices);
};
const inputMap = [
{ name: "Joe", num: 9 },
{ name: "Cami", num: 3 },
{ name: "Cassidy", num: 4 }
];
console.log(gimmePizza(inputMap, 8));
// https://codesandbox.io/s/young-darkness-61nq3?file=/src/index.ts/**
* Given a positive integer n, write a function that returns
* true if it is a perfect square and false otherwise.
* Don’t use any built-in math functions like sqrt.
* Hint: Use binary search!
*
* Examples:
* $ perfectSquare(25)
* $ true
*
* $ perfectSquare(10)
* $ false
*/
const isPerfectSquare = (input: number) => {
const binarySearchPerfectSquare = (
input: number,
start: number,
end: number
): number | boolean => {
if (start > end) return false;
// mid value, parsed to an int using bitwise operator
const mid = ((start + end) / 2) >> 0;
if (mid * mid < input)
return binarySearchPerfectSquare(input, mid + 1, end);
if (mid * mid > input)
return binarySearchPerfectSquare(input, start, mid - 1);
// mid*mid === input, perfect square!
return true;
};
return binarySearchPerfectSquare(input, 1, input);
};
console.log(isPerfectSquare(25));
console.log(isPerfectSquare(10));
// https://codesandbox.io/s/relaxed-pine-yofdz?file=/src/index.ts/**
* Given an array of integers and a target value, return the number of
* pairs of array elements that have a difference equal to a target value.
*
* Example:
* $ arrayDiff([1, 2, 3, 4], 1)
* $ 3 // 2 - 1 = 1, 3 - 2 = 1, and 4 - 3 = 1
*/
const arrayDiff = (arr: Array<number>, target: number) => {
let count = 0,
flag = false;
arr.sort()
.reverse()
.forEach((baseNum, i, reverseSortedArr) => {
if (i === arr.length) return;
flag = false;
reverseSortedArr.slice(i + 1).forEach((num, j) => {
// arr is sorted, so we won't get the target diff again
if (flag) return;
if (j === reverseSortedArr.length) return;
if (baseNum - num === target) {
count += 1;
flag = true;
}
});
});
return count;
};
console.log(arrayDiff([1, 2, 3, 4], 1));
// https://codesandbox.io/s/cool-satoshi-84ku4?file=/src/index.ts/**
* You’re given a string of characters that are only 2s and 0s. Return the
* index of the first occurrence of “2020” without using the indexOf (or
* similar) function, and -1 if it’s not found in the string.
*
* Example:
* $ find2020(‘2220000202220020200’)
* $ 14
*/
const find2020 = (input: string) => {
let index = -1;
input.split("").reduce((_shouldBe2020, _curr, i) => {
const next4 = input.slice(i, i + 4);
if (next4 === "2020") index = i;
return next4;
}, input.slice(0, 4));
return index;
};
// https://codesandbox.io/s/sharp-mountain-wddiy?file=/src/index.ts/**
* Given a rowIndex, return an array of the values in that
* row of Pascal’s Triangle.
*/
const getCurrentRow = (previousRow: Array<number>): Array<number> => {
return Array.from(Array(previousRow.length + 1)).map((_, i) => {
if (i === 0) return 1;
else if (i === previousRow.length) return 1;
else return previousRow[i - 1] + previousRow[i];
});
};
const getPascalRow = (index: number): Array<number> => {
if (index === 0) return [1];
return getCurrentRow(getPascalRow(index - 1));
};
console.log(getPascalRow(0)); // [1]
console.log(getPascalRow(1)); // [1, 1]
console.log(getPascalRow(2)); // [1, 2, 1]
console.log(getPascalRow(3)); // [1, 3, 3, 1]
console.log(getPascalRow(4)); // [1, 4, 6, 4, 1]
// https://codesandbox.io/s/heuristic-wood-qzzbd?file=/src/index.ts/**
* Given an integer n, return true if n^3 and n have the same set of digits.
* Example:
*
* $ sameDigits(1) // true
* $ sameDigits(10) // true
* $ sameDigits(251894) // true
* $ sameDigits(251895) // false
*/
const INPUTS = [1, 10, 251894, 251895];
const getUniqueDigitsAsString = (input: number) =>
[...new Set(input.toString().split("").sort())].join();
const sameDigits = (input: number) => {
const inputDigits = getUniqueDigitsAsString(input);
const cubeDigits = getUniqueDigitsAsString(Math.pow(input, 3));
return inputDigits === cubeDigits;
};
INPUTS.forEach(input => console.log(sameDigits(input)))
// true, true, true, false
// https://codesandbox.io/s/cold-cdn-85qcb?file=/src/index.ts/**
* Given a list, return a list of all its prefixes in ascending order of their
* length. You’re essentially implementing the inits function in Haskell!
*
* Example:
* $ inits([4, 3, 2, 1])
* $ [[], [4], [4,3], [4,3,2], [4,3,2,1]]
*
* $ inits([144])
* $ [[], [144]]
*/
const INPUT = [4, 3, 2, 1];
const inits = (input: Array<number>) =>
input.reduce(
(arr, curr, index) => {
arr.push([...arr[index], curr]);
return arr;
},
[[]] as number[][]
);
console.log(inits(INPUT));
// https://codesandbox.io/s/determined-swanson-qn27b?file=/src/index.ts/**
* Given a direction and a number of columns, write a function that outputs an
* arrow of asterisks (see the pattern in the examples below)!
*
* Example:
*
* $ printArrow('right', 3)
* Output:
*
*
*
*
*
* $ printArrow('left', 5)
* Output:
*
*
*
*
*
*
*
*
*
*/
const printArrow = (direction: "right" | "left", len: number) => {
Array.from(Array(2 * (len - 1) + 1)).forEach((_, index) => {
let numSpaces;
if (direction === "right") {
numSpaces = index > len - 1 ? 2 * len - 2 - index : index;
} else {
numSpaces = len - (index > len - 1 ? 2 * len - 1 - index : index + 1);
}
console.log(`${" ".repeat(numSpaces)}*`);
});
};
// https://codesandbox.io/s/gifted-perlman-0yvo0?file=/src/index.tsconst LINE = "█".repeat(10);
const PRIDE_COLORS = [
"#e40303",
"#ff8c00",
"#ffed00",
"#008026",
"#004dff",
"#750787"
];
const PrideFlag = () => {
PRIDE_COLORS.forEach((color) => {
console.log(`%c${LINE}`, `color: ${color}`);
});
};
PrideFlag();
// https://codesandbox.io/s/blissful-leavitt-86k1s?file=/src/index.ts/**
* Write a function to find the longest common prefix string in an array of
* strings.
*
* Example:
*
* $ longestPrefix(["cranberry","crawfish","crap"])
* $ "cra"
*
* $ longestPrefix(["parrot", "poodle", "fish"])
* $ ""
*/
function longestPrefix(input: Array<string>) {
let result = "";
input[0].split("").reduce((prefix, currentLetter) => {
const isPrefixValid = input.every((word) => word.startsWith(prefix));
if (isPrefixValid) {
result = prefix;
return `${prefix}${currentLetter}`;
}
return result;
}, "");
return result;
}
// https://codesandbox.io/s/heuristic-dan-pl0nn?file=/src/index.ts/**
* An “odious number” is a non-negative number that has an
* odd number of 1s in its binary expansion. Write a
* function that returns true if a given number is odious.
*
* Example:
*
* $ isOdious(14)
* $ true
*
* $ isOdious(5)
* $ false
*/
const isOdious = (input: number) =>
(input.toString(2).match(/1/g) ?? []).length % 2 === 1;
// https://codesandbox.io/s/admiring-poitras-8l6sd?file=/src/index.ts/**
* Given an array of objects A, and an array of indexes B,
* reorder the objects in array A with the given indexes
* in array B.
*
* Example:
*
* let a = [C, D, E, F, G, H];
* let b = [3, 0, 4, 1, 2, 5];
*
* $ reorder(a, b) // a is now [D, F, G, C, E, H]
*/
const reorder = (
a: Array<Record<string, unknown> | string>,
b: Array<number>
) =>
[...Array(a.length)].reduce((res, _, index) => {
res[b[index]] = a[index];
return res;
}, []);
// https://codesandbox.io/s/agitated-bash-tmu25?file=/src/index.tsdefmodule RWC_259 do
@doc """
Given an integer n, count the total number of 1 digits appearing in all
non-negative integers less than or equal to n.
Example:
> numberOfOnes(14)
> 7 // 1, 10, 11, 12, 13, 14
"""
defp count_one_recursively(input, count) when input == 1, do: count + 1
defp count_one_recursively(input, count) do
input
|> Integer.to_string()
|> String.split("")
|> Enum.count(&(&1 == "1"))
|> then(fn x ->
case x > 0 do
true ->
count_one_recursively(input - 1, count + x)
_ ->
count_one_recursively(input - 1, count)
end
end)
end
def number_of_ones(input) do
input
|> count_one_recursively(0)
|> IO.puts()
end
end
RWC_259.number_of_ones(14)defmodule RWC_270 do
@doc """
Let’s say you have n doors that start out as closed. With the first pass
across the doors, you toggle every door open. With the second pass, you
toggle every second door. With the third, every third door, and so on.
Write a function that takes in an integer numberOfPasses, and returns how
many doors are open after the number of passes.
Example:
let n = 7
let numberOfPasses = 3
> passDoors(n, numberOfPasses)
> 4
// Explanation:
// 0 means open, 1 means closed
// Initial: 1 1 1 1 1 1 1
// Pass 1: 0 0 0 0 0 0 0
// Pass 2: 0 1 0 1 0 1 0
// Pass 3: 0 1 1 1 0 0 0
"""
@spec pass_doors(n :: non_neg_integer, number_of_passes :: non_neg_integer) :: non_neg_integer
def pass_doors(n, number_of_passes) do
1..number_of_passes
# duplicate with n+1 because map_every/3 starts from first elem indexed 0
# open => true, closed => false
|> Enum.reduce(List.duplicate(false, n + 1), fn nth, doors ->
Enum.map_every(doors, nth, &(not &1))
end)
# ignore the extra door we added at the start
|> Enum.drop(1)
|> Enum.count(& &1)
end
end
RWC_270.pass_doors(7, 3)defmodule RWC_281 do
@doc """
Given an array of integers arr and an integer n, return a subarray
of arr of length n where the sum is the largest.
Make sure you maintain the order of the original array, and if n
is greater than arr.length, you can choose what you want to return.
> maxSubarray([-4,2,-5,1,2,3,6,-5,1], 4)
> [1,2,3,6]
> maxSubarray([1,2,0,5], 2)
> [0,5]
"""
def maxSubarray(input, size) do
input
|> Enum.chunk_every(size, 1, :discard)
|> Enum.max_by(&Enum.sum(&1))
end
end
IO.inspect(RWC_281.maxSubarray([-4, 2, -5, 1, 2, 3, 6, -5, 1], 4))
IO.inspect(RWC_281.maxSubarray([1, 2, 0, 5], 2))defmodule RWC_282 do
@doc """
Given a number, sum every second digit in that number.
Example:
> sumEveryOther(548915381)
> 26 // 4+9+5+8
> sumEveryOther(10)
> 0
> sumEveryOther(1010.11)
> 1 // 0+0+1
"""
def sumEveryOther(input) do
input
|> to_string()
|> String.graphemes()
|> List.delete_at(0)
|> Enum.filter(&(&1 !== "."))
|> Enum.take_every(2)
|> Enum.map(&String.to_integer/1)
|> Enum.sum()
end
enddefmodule RWC_284 do
@doc """
You are given a list of positive integers which represents some
range of integers which has been truncated. Find the missing bits,
insert ellipses to show that that part has been truncated, and
print it. If the consecutive values differ by exactly two,
then insert the missing value.
Examples:
> missingBits([1,2,3,4,20,21,22,23])
> "[1,2,3,4,...,20,21,22,23]"
> missingBits([1,2,3,5,6])
> "[1,2,3,4,5,6]"
> missingBits([1,3,20,27])
> "[1,2,3,...,20,...,27]"
"""
def missingBits(input) do
input
|> Enum.with_index()
|> then(fn input_with_index ->
input_with_index
|> Enum.reduce([], fn {num, index}, acc ->
{next_num, _} = Enum.at(input_with_index, index + 1, {num, nil})
case next_num - num do
# Last index
0 -> [num | acc]
1 -> [num | acc]
# When step is exactly two
2 -> [num + 1, num | acc]
_ -> ["...", num | acc]
end
end)
|> Enum.reverse()
|> Enum.join(",")
|> then(&"[#{&1}]")
end)
end
enddefmodule RWC_285 do
@doc """
Given a positive integer, generate an array in which every
element is an array that goes from 1 to the index of that array.
Example:
> generateArrays(4)
> [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4]]
> generateArrays(1)
> [[1]]
"""
def generateArrays(input) do
1..input
|> Enum.to_list()
|> Enum.map(&Enum.to_list(1..&1))
end
enddefmodule RWC_286 do
@doc """
Spreadsheet programs often use the A1 Reference Style to refer to columns.
Given a column name in this style, return its column number.
Examples of column names to their numbers:
A -> 1
B -> 2
C -> 3
// etc
Z -> 26
AA -> 27
AB -> 28
// etc
AAA -> 703
"""
def get_weight(char, power) do
char
|> String.to_charlist()
|> hd()
# A => 65, B => 66, so on...
|> then(&(&1 - 64))
|> then(&(&1 * 26 ** power))
end
def recusively_get_weight([{char, index}]), do: get_weight(char, index)
def recusively_get_weight([left | rest]),
do: recusively_get_weight([left]) + recusively_get_weight(rest)
def get_column_number(input) do
input
|> String.split("", trim: true)
|> Enum.reverse()
|> Enum.with_index()
|> recusively_get_weight()
end
enddefmodule RWC_287 do
@doc """
Print the digits 0 through 100 without using the characters
1, 2, 3, 4, 5, 6, 7, 8, or 9 in your code. Get creative!
"""
def print_digits() do
hundred =
"d"
|> to_charlist()
|> hd()
zero =
[hundred - hundred]
|> hd()
zero..hundred
|> Enum.join(", ")
end
enddefmodule RWC_288 do
@doc """
Given a string of parenthesis, return the number of parenthesis
you need to add to the string in order for it to be balanced.
Examples:
> numBalanced(`()`)
> 0
> numBalanced(`(()`)
> 1
> numBalanced(`))()))))()`)
> 6
> numBalanced(`)))))`)
> 5
"""
def num_balanced(input) do
input
|> String.split("", trim: true)
|> Enum.frequencies()
|> Map.values()
|> then(
&case &1 do
[only_one_kind] -> only_one_kind
[one, other] -> abs(one - other)
end
)
end
enddefmodule RWC_289 do
@doc """
Given a list of numbers, return all groups of repeating consecutive numbers.
Examples:
> repeatedGroups([1, 2, 2, 4, 5])
[[2, 2]]
> repeatedGroups([1, 1, 0, 0, 8, 4, 4, 4, 3, 2, 1, 9, 9])
[[1, 1], [0, 0], [4, 4, 4], [9, 9]]
"""
def chunk_repeats([head | rest]), do: chunk_repeats(rest, [[head]])
def chunk_repeats([], done), do: done
def chunk_repeats([head | rest], [[head | head_repeated] | previously_repeated]),
do: chunk_repeats(rest, [[head | [head | head_repeated]] | previously_repeated])
def chunk_repeats([head | rest], previously_repeated),
do: chunk_repeats(rest, [[head] | previously_repeated])
def repeated_groups(input) do
input
|> chunk_repeats()
|> Enum.reverse()
|> Enum.filter(&(length(&1) > 1))
end
enddefmodule RWC_300 do
@doc """
Write a function to find out whether the binary representation of
a number is palindrome or not.
Example:
> binaryPal(5)
> true
> binaryPal(10)
> false
"""
def binary_pal(input) do
input
|> Integer.to_charlist(2)
|> List.to_string()
|> then(fn digits ->
digits
|> String.reverse()
|> then(
&case &1 do
^digits -> true
_ -> false
end
)
end)
end
enddefmodule RWC_301 do
@doc """
Given a string, calculate the score that it would get in a game of Scrabble.
For extra credit, try verifying if the string is a valid word, or take into
account premium squares!
Scoring and example:
1 point: E, A, I, O, N, R, T, L, S, U
2 points: D, G
3 points: B, C, M, P
4 points: F, H, V, W, Y
5 points: K
8 points: J, X
10 points: Q, Z
> scrabbleScore('FIZZBUZZ')
> 49
"""
@score_map %{
"EAIONRTLSU" => 1,
"DG" => 2,
"BCMP" => 3,
"FHVWY" => 4,
"K" => 5,
"JX" => 8,
"QZ" => 10
}
def scrabble_score(input) do
input
|> String.split("", trim: true)
|> Enum.reduce(0, fn letter, score ->
@score_map
|> Map.keys()
|> Enum.find(&String.contains?(&1, letter))
|> then(&Map.get(@score_map, &1))
|> Kernel.+(score)
end)
end
enddefmodule RWC_303 do
@doc """
Given an array of people objects (where each person has a name and a number of
pie pieces they’re hungry for) and a number for the number of pieces that the
pie can be cut into, return the number of pies you need to buy.
Example:
iex>
...> arr = [
...> %{ name: Joe, num: 9 },
...> %{ name: Cami, num: 3 },
...> %{ name: Cassidy, num: 4 }
...> ]
iex> RWC_303.num_pie(arr, 8)
2 # 16 pieces needed, pies can be cut into 8 pieces, so 2 pies should be bought
"""
def num_pie(input, count) do
input
|> Enum.reduce(0, &(&2 + &1[:num]))
|> div(count)
end
enddefmodule RWC_304 do
@doc """
Given an array arr and integers n and m, remove n elements
from the front of the array, and m elements from the back.
Assume that n + m <= arr.length.
Example:
iex> RWC_304.trim_array([1, 2, 3, 4, 5, 6], 2, 1)
[3, 4, 5]
iex> RWC_304.trim_array([6, 2, 4, 3, 7, 1, 3], 5, 0)
[1, 3]
iex> RWC_304.trim_array([1, 7], 0, 0)
[1, 7]
"""
def trim_array(input, n, m) do
input
|> Enum.slice(n, length(input) - n - m)
end
enddefmodule RWC_305 do
@doc """
Given some JSON data, calculate the maximum depth reached. Both arrays
and dictionaries increase the depth! If the input is invalid data, the
response should be undefined (you decide how you want that to return).
iex> RWC_305.depth_json([])
1
iex> RWC_305.depth_json([1, 2, 3, 4, 5])
1
iex> RWC_305.depth_json([%{a: []}, ["abc"]])
3
"""
def depth_json(input), do: compute_depth(input)
defp compute_depth(input) when is_list(input) or is_map(input) do
cond do
is_list(input) and input == [] ->
1
true ->
input
|> flatten_if_map()
|> Enum.map(&compute_depth/1)
|> Enum.max()
|> Kernel.+(1)
end
end
defp compute_depth(_), do: 0
defp flatten_if_map(input) when is_map(input), do: Map.values(input)
defp flatten_if_map(input), do: input
end
defmodule RWC_306 do
@doc """
Write a function that takes an array of consecutive, increasing letters as input,
and returns any missing letters in the array between the first and last letter.
Example:
iex> RWC_306.missing_letters(["a","b","c","d","f"])
["e"]
iex> RWC_306.missing_letters(["a","b","c","d","e","h","i","j","k","l","m","n","o",
...> "p","q","r","s","t","u","w","x","y","z"])
["f","g","v"]
"""
def missing_letters(input) do
input_complete_mapset =
input
|> then(fn list ->
[head | _] = list
tail = List.last(list)
hd(to_charlist(head))..hd(to_charlist(tail))
|> MapSet.new()
end)
input_mapset =
input
|> MapSet.new(&hd(to_charlist(&1)))
input_complete_mapset
|> MapSet.difference(input_mapset)
|> MapSet.to_list()
|> List.to_string()
|> String.graphemes()
end
enddefmodule RWC_307 do
@doc """
Given an integer n, return true if it's a perfect
square AND when reversed, is still a perfect square.
iex> RWC_307.reversed_squares(9)
true
iex> RWC_307.reversed_squares(441)
true
iex> RWC_307.reversed_squares(25)
false
"""
def reversed_squares(input) do
input
|> Integer.digits()
|> Enum.reverse()
|> Integer.undigits()
|> then(
&cond do
is_perfect_square(&1) and is_perfect_square(input) -> true
true -> false
end
)
end
defp is_perfect_square(input) do
input
|> :math.sqrt()
|> then(&if Kernel.trunc(&1) == &1, do: true, else: false)
end
enddefmodule RWC_308 do
@doc """
Given an array of strings and a max width, format the text such that each line has exactly
maxWidth characters and is fully justified. You can choose how you want to wrap a word.
Example:
iex> RWC_308.justify_text(["This", "is", "an", "example", "of", "text", "justification."], 16)
[
"This is an",
"example of text",
"justification. "
]
"""
def justify_text(input, max_length) do
input
|> Enum.reduce([[]], fn word, phrase_list ->
phrase_list
|> List.last([])
|> then(fn last_phrase ->
current_phrase_length = last_phrase |> Enum.join(".") |> String.length()
cond do
current_phrase_length + String.length(word) < max_length ->
# update last element
last_list =
phrase_list
|> Enum.at(-1)
|> Enum.concat([word])
phrase_list
|> Enum.drop(-1)
|> Enum.concat([last_list])
true ->
# move to new phrase
phrase_list
|> Enum.concat([[word]])
end
end)
end)
|> Enum.map(&justify_phrase(&1, max_length))
end
defp justify_phrase(input, max_length) do
number_of_spaces_to_add = max_length - (input |> Enum.join("") |> String.length())
number_of_breaks = if length(input) == 1, do: 1, else: length(input) - 1
each_space_block_length = div(number_of_spaces_to_add, number_of_breaks)
remainder = rem(number_of_spaces_to_add, number_of_breaks)
spaces_list =
" "
|> list_from(each_space_block_length)
|> list_from(number_of_breaks)
|> then(fn [first_break_spaces | rest] ->
case remainder do
0 ->
[first_break_spaces | rest]
_ ->
first_break_spaces
|> Enum.concat(list_from(" ", remainder))
|> then(&[&1 | rest])
end
end)
|> then(
&cond do
length(input) == 1 -> &1
true -> Enum.concat(&1, [[""]])
end
)
input
|> Enum.zip(spaces_list)
|> Enum.reduce("", fn {word, spaces}, line ->
"#{line}#{word}#{Enum.join(spaces)}"
end)
end
defp list_from(el, count), do: for(_ <- 1..count, do: el)
enddefmodule RWC_309 do
@doc """
Given a string, separate it into groups of non-space equal characters, sorted.
Example:
iex> RWC_309.explode_string("Ahh, abracadabra!")
["!",",","A","aaaaa","bb","c","d","hh","rr"]
"""
def explode_string(input) do
input
|> String.replace(" ", "")
|> String.split("", trim: true)
|> Enum.frequencies()
|> Map.to_list()
|> Enum.map(fn {char, count} ->
list_from(char, count)
|> Enum.join()
end)
end
defp list_from(el, count), do: for(_ <- 1..count, do: el)
enddefmodule RWC_310 do
@doc """
Given an array where each element is the price of a given stock on that index's day,
choose a single day to buy a stock and a different day (in the future/later in the array)
to sell the stock to maximize your profit. Return the maximum profit that you can get
from a given input. If you can't profit, return 0.
Example:
iex> RWC_310.maximum_profit([7, 1, 5, 3, 6, 4])
5 # Buy on day 2, and sell on day 5, your profit = 6 - 1 = 5.
"""
def maximum_profit(input) do
input
|> Enum.with_index()
|> Enum.reduce(0, fn {price, index}, max_profit ->
input
|> Enum.slice((index + 1)..-1)
|> Enum.max(&>=/2, fn -> 0 end)
|> Kernel.-(price)
|> then(
&cond do
&1 > max_profit -> &1
true -> max_profit
end
)
end)
end
enddefmodule RWC_311 do
@doc """
Given two strings s and t, return true if t is an anagram of s, and false otherwise.
Try this in a language you're not comfortable with!
Example:
iex> RWC_311.is_anagram("barbie", "oppenheimer")
false
iex> RWC_311.is_anagram("race", "care")
true
"""
def is_anagram(a, b), do: get_chars(a) === get_chars(b)
defp get_chars(input), do: input |> String.split("", trim: true) |> Enum.frequencies()
enddefmodule RWC_312 do
@doc """
Implement the Luhn algorithm to validate a credit card number.
Bonus points if you can identify what brand of credit card the user inputted!
iex> RWC_312.luhn_check(123456789)
false
iex> RWC_312.luhn_check(5555555555554444)
true
"""
def luhn_check(input) do
input
|> Integer.digits()
|> Enum.with_index(1)
|> Enum.reduce(0, fn {digit, index}, sum ->
cond do
rem(index, 2) == 0 -> digit * 2
true -> digit
end
|> Integer.digits()
|> Enum.sum()
|> Kernel.+(sum)
end)
|> then(&(rem(&1, 10) == 0))
end
enddefmodule RWC_313 do
@doc """
You have a faulty keyboard. Whenever you type a vowel on it (a,e,i,o,u,y),
it reverses the string that you have written, instead of typing the character.
Typing other characters works as expected. Given a string, return what will be
on the screen after typing with your faulty keyboard.
Example:
iex> RWC_313.faulty_keeb("string")
"rtsng"
iex> RWC_313.faulty_keeb("hello world!")
"w hllrld!"
"""
@vowels ["a", "e", "i", "o", "u", "y"]
def faulty_keeb(input) do
input
|> String.graphemes()
|> Enum.reduce([], fn char, word ->
cond do
Enum.member?(@vowels, char) -> Enum.reverse(word)
true -> Enum.concat(word, [char])
end
end)
|> Enum.join()
end
enddefmodule RWC_314 do
@doc """
Make a "guessing game" where there is a target number, and as the user makes
guesses, the output returns higher or lower until the user is correct.
Example usage:
Guess the number!
> 10
higher
> 20
higher
> 30
lower
> 25
higher
> 27
Correct! You won in 5 guesses!
"""
def solve(guess) do
IO.puts("Guess the number!")
input()
|> solve(guess)
end
def solve(guess, answer, guess_count \\ 1)
def solve(guess, answer, 1) when guess === answer,
do: IO.puts("Correct! You won in 1 guess!") |> exit()
def solve(guess, answer, guess_count) when guess === answer,
do: IO.puts("Correct! You won in #{guess_count} guesses!") |> exit()
def solve(guess, answer, guess_count) do
cond do
guess > answer ->
IO.puts("lower")
guess < answer ->
IO.puts("higher")
end
input()
|> solve(answer, guess_count + 1)
end
defp input() do
IO.gets("> ")
|> Integer.parse()
|> then(&elem(&1, 0))
end
end
RWC_314.solve(:rand.uniform(100))defmodule RWC_315 do
@moduledoc """
Given a sequence of numbers, generate a "count and say" string.
Example:
iex> RWC_315.count_and_say(112222555)
"two 1s, then four 2s, then three 5s"
iex> RWC_315.count_and_say(3333333333)
"ten 3s"
"""
@number_say_map %{
1 => "one",
2 => "two",
3 => "three",
4 => "four",
5 => "five",
6 => "six",
7 => "seven",
8 => "eight",
9 => "nine",
10 => "ten"
}
def count_and_say(input) do
input
|> Integer.digits()
# count
|> Enum.reduce([], fn number, list ->
current_list = List.first(list, [nil])
current_list
|> List.first()
|> then(fn current_digit ->
case current_digit do
# same digit as current
^number ->
list
|> List.delete_at(0)
|> then(&[[number | current_list] | &1])
# new digit
_ ->
[[number] | list]
end
end)
end)
|> Enum.reverse()
# say
|> Enum.map_join(", then ", fn list ->
len = Map.get(@number_say_map, length(list))
"#{len} #{List.first(list)}s"
end)
end
enddefmodule RWC_316 do
@moduledoc """
Given an array of integers and a number k (where k is guaranteed to be less
than the array's length), return a subarray of length k with the minimum
possible sum. Maintain the order of the original array!
Example:
iex> RWC_316.min_subs([1, 3, 20, 4, 8, 9, 11], 3)
[4, 8, 9]
iex> RWC_316.min_subs([4, 4, 4, 4, 8], 2)
[4, 4]
"""
def min_subs(input, len) do
input
|> Enum.chunk_every(len, 1, :discard)
|> Enum.min_by(&Enum.sum/1)
end
enddefmodule RWC_317 do
@moduledoc """
Given an array of integers, sort them into two separate sorted
arrays of even and odd numbers. If you see a zero, skip it.
Example:
iex> RWC_317.separate_and_sort([4, 3, 2, 1, 5, 7, 8, 9])
[[2, 4, 8], [1, 3, 5, 7, 9]]
iex> RWC_317.separate_and_sort([1,1,1,1])
[[], [1,1,1,1]]
"""
def separate_and_sort(input) do
input
|> Enum.sort()
|> Enum.split_with(&(rem(&1, 2) == 0))
|> Tuple.to_list()
end
enddefmodule RWC_318 do
@moduledoc """
You have n equal-sized blocks and you want to build a staircase
with them. Return the number of steps you can fully build.
iex> RWC_318.build_staircase(6)
3
#=> #
#=> ##
#=> ###
iex> RWC_318.build_staircase(9)
3 #=> it takes 10 blocks to make 4 steps
"""
def build_staircase(input) do
1..input
|> Enum.reduce_while(0, fn step, total ->
cond do
total + step > input -> {:halt, step - 1}
true -> {:cont, total + step}
end
end)
end
enddefmodule RWC_322 do
@moduledoc """
Given two strings s and t, determine if they are isomorphic.
Two strings are isomorphic if there is a one-to-one mapping
possible for every character of the first string to every
character of the second string.
iex> RWC_322.is_isomorphic("abb", "cdd")
true # "a" maps to "c" and "b" maps to "d"
iex> RWC_322.is_isomorphic("cassidy", "1234567")
false # "s" cannot have a mapping to both "3" and "4"
iex> RWC_322.is_isomorphic("cass", "1233")
true
"""
def is_isomorphic(first, second) do
[first, second]
|> Enum.map(fn string ->
string
|> String.split("", trim: true)
|> Enum.frequencies()
|> Map.values()
end)
|> then(fn [f1, f2] -> f1 == f2 end)
end
enddefmodule RWC_323 do
@moduledoc """
Given a string s, you are allowed to delete at most k characters.
Find if the string can be a palindrome after deleting at most k characters.
iex> RWC_323.k_pal("abcweca", 2)
true
iex> RWC_323.k_pal("abcweca", 1)
false
iex> RWC_323.k_pal("acwca", 2)
true
iex> RWC_323.k_pal("acxcb", 1)
false
"""
def k_pal(string, count) do
string
|> String.graphemes()
|> check_first_and_last_characters(count)
end
defp check_first_and_last_characters([_char], _count), do: true
defp check_first_and_last_characters([char | [char]], _count), do: true
defp check_first_and_last_characters(string, count) do
[first | with_last] = string
[last | remaining_reversed] = Enum.reverse(with_last)
remaining = Enum.reverse(remaining_reversed)
cond do
first == last ->
check_first_and_last_characters(remaining, count)
first != last and count == 0 ->
false
first != last and count > 0 ->
check_first_and_last_characters([first | remaining], count - 1) or
check_first_and_last_characters(with_last, count - 1)
true ->
false
end
end
enddefmodule RWC_325 do
@moduledoc """
Given a list of words and a dictionary of letter scores, find
the word with the highest score according to the rules:
score = word_length * (sum of letter scores in the word)
If there are multiple words with the same highest score,
return the lexicographically smallest one.
iex> word_list = ["apple", "banana", "cherry", "date", "fig"];
...> RWC_325.score_word_game(word_list)
"cherry"
"""
def score_word_game(word_list, _letter_scores \\ nil) do
word_list
|> Enum.map(&get_word_score/1)
|> Enum.max_by(fn {_word, score} -> score end)
|> then(&elem(&1, 0))
end
defp get_word_score(word) do
word
|> String.downcase()
|> String.graphemes()
|> Enum.reduce(0, fn letter, total ->
score = (to_charlist(letter) |> hd()) - 96
total + score
end)
|> then(&{word, &1})
end
enddefmodule RWC_326 do
@moduledoc """
Given a list of tasks, where each task has a duration, and a limited amount
of available time to work, write a function to return the tasks that can be
completed within the given time, without re-ordering the original list of tasks.
Try to maximize the number of tasks that can be completed!
Example:
iex> tasks = [
...> %{ name: "Task 1", duration: 4 },
...> %{ name: "Task 2", duration: 2 },
...> %{ name: "Task 3", duration: 7 },
...> %{ name: "Task 4", duration: 5 },
...> %{ name: "Task 5", duration: 1 },
...> %{ name: "Task 6", duration: 3 }
...> ];
...> time_to_work = 6;
...> RWC_326.do_tasks(tasks, time_to_work)
["Task 2", "Task 5", "Task 6"]
"""
def do_tasks(task_list, time_to_work) do
task_list
|> Enum.with_index()
|> Enum.sort_by(fn {%{duration: duration}, _index} -> duration end)
|> Enum.reduce_while({0, []}, fn {%{duration: duration}, index}, {time_sum, indices} ->
cond do
time_sum + duration > time_to_work -> {:halt, indices}
true -> {:cont, {time_sum + duration, [index | indices]}}
end
end)
|> Enum.sort()
|> Enum.map(
&(task_list
|> Enum.at(&1)
|> then(fn %{name: name} -> name end))
)
end
enddefmodule RWC_327 do
@moduledoc """
Given a start number a, an ending number b, and a string str that can
be "odd", "even", or "prime", return all of the numbers that are odd, even,
or prime between a and b. a will not always necessarily be less than b!
iex> RWC_327.between_nums(3, 11, "even")
[4,6,8,10]
iex> RWC_327.between_nums(15, 1, "prime")
[2,3,5,7,11,13]
"""
defp is_prime(num) do
cond do
num <= 1 ->
false
num == 2 ->
true
rem(num, 2) == 0 ->
false
true ->
3..(num - 1)//2
|> Enum.all?(&(rem(num, &1) != 0))
end
end
def between_nums(start, finish, option) when start > finish,
do: between_nums(finish, start, option)
def between_nums(start, finish, option) do
start..finish
|> Enum.filter(fn num ->
case option do
"prime" ->
is_prime(num)
"even" ->
rem(num, 2) == 0
_ ->
rem(num, 2) != 0
end
end)
end
enddefmodule RWC_328 do
@moduledoc """
Given two arrays calories and prices, where calories[i] and prices[i]
represent the calorie content and price of the ith food item, and a
daily calorie goal, find the minimum cost to achieve or exceed the daily
calorie goal. If it's impossible to meet the goal, return -1.
Example:
iex> calories = [200, 400, 600, 800]
...> prices = [50, 60, 80, 100]
...> daily_goal = 1200
...> RWC_328.min_cost_for_calories(calories, prices, daily_goal)
160 # the 2nd and 4th items add up to 1200 calories for the minimum cost
"""
def min_cost_for_calories(calories, prices, daily_goal) do
calories
|> Enum.with_index()
|> Enum.flat_map(fn {calorie, index} ->
calories
|> Enum.with_index()
|> Enum.slice(index..-1)
|> Enum.filter(&(elem(&1, 0) != calorie))
|> Enum.map(&{elem(&1, 0) + calorie, {index, elem(&1, 1)}})
end)
|> Enum.filter(&(elem(&1, 0) >= daily_goal))
|> Enum.reduce(:infinity, fn {_calories, {index_a, index_b}}, total_price ->
current_combo_price = Enum.at(prices, index_a) + Enum.at(prices, index_b)
cond do
current_combo_price < total_price -> current_combo_price
true -> total_price
end
end)
end
enddefmodule RWC_329 do
@moduledoc """
There is a sorted integer array that has been rotated an unknown number of times.
Given that rotated array, return how many times it has been rotated.
It may contain duplicate numbers!
iex> RWC_329.rotated_num([4, 0, 1, 2, 3])
1
iex> RWC_329.rotated_num([7, 9, 20])
0
iex> RWC_329.rotated_num([7, 7, 314, 1337, 7])
4
"""
def rotated_num(nums) do
cond do
Enum.sort(nums) == nums -> 0
true -> 1 + rotated_num(Enum.slide(nums, 0, -1))
end
end
enddefmodule RWC_330 do
@moduledoc """
Given an array of integers, return the majority element. If there is no
majority element, return if the array is majority even or odd numbers,
and if there is none, say so.
iex> RWC_330.majority([3,1,4,1])
"1"
iex> RWC_330.majority([33,44,55,66,77])
"Majority odds"
iex> RWC_330.majority([1,2,3,4])
"No majority"
"""
def majority(nums) do
nums
|> Enum.frequencies()
|> Map.to_list()
|> Enum.sort_by(fn {_, count} -> count end, :desc)
|> then(fn [{possible_majority, first} | [{_, second} | _]] ->
cond do
first == second ->
nums
|> Enum.group_by(&(rem(&1, 2) == 0))
|> then(fn %{false: odds, true: evens} ->
cond do
length(odds) > length(evens) -> "Majority odds"
length(odds) > length(evens) -> "Majority evens"
true -> "No majority"
end
end)
true ->
Integer.to_string(possible_majority)
end
end)
end
enddefmodule RWC_331 do
@moduledoc """
Write a function that determines if an array of numbers is a bitonic sequence.
A bitonic sequence is a sequence of numbers in which the numbers are in
increasing order, and after a certain point, they start decreasing.
Extra credit: print the peak number in the sequence!
iex> RWC_331.is_bitonic([1,2,3,2])
3 # true, extra credit: 3
iex> RWC_331.is_bitonic([1,2,3])
false
iex> RWC_331.is_bitonic([3,4,5,5,5,2,1])
5 # true, extra credit: 5
"""
def is_bitonic(list) do
list
|> Enum.reduce_while({Enum.at(list, 0), :asc}, fn num, {peak, trend} ->
cond do
num >= peak and trend == :asc -> {:cont, {num, :asc}}
num < peak and trend == :asc -> {:cont, {peak, :desc}}
num < peak and trend == :desc -> {:cont, {peak, :desc}}
true -> {:halt, {peak, :err}}
end
end)
|> then(fn
{_, :err} -> false
{_, :asc} -> false
{peak, :desc} -> peak
end)
end
enddefmodule RWC_332 do
@moduledoc """
You have some gifts you want to return. Gifts bought in December have a
90-day return window, and all other gifts have a 30-day return window.
Given a gift's buy date, write a function that prints the last day you
can return the gift. You can choose how dates should be formatted!
# Given date: "Dec 25, 2023"
iex> RWC_332.return_gift("2023-12-25")
"2024-03-23" # 90 days
iex> RWC_332.return_gift("2023-11-25")
"2023-12-24" # 30 days
"""
def return_gift(date) do
date
|> String.split("-")
|> case do
# December
[_, "12", _] -> 90 - 1
_ -> 30 - 1
end
|> then(fn days ->
date
|> Date.from_iso8601!()
|> Date.add(days)
|> Date.to_iso8601()
end)
end
enddefmodule RWC_333 do
@moduledoc """
Write a program that prints Happy new year! without using the
string/character literals for the characters in the string!
iex> RWC_333.wish_happy_new_year()
"Happy New Year"
"""
def wish_happy_new_year() do
# Charlist
[72, 97, 112, 112, 121, 32, 78, 101, 119, 32, 89, 101, 97, 114]
|> to_string()
end
enddefmodule RWC_334 do
@moduledoc """
You have an array of letters. Return the number of possible sequences of
letters you can make using the letters in the array.
Extra credit: print the sequences!
iex> RWC_334.letters(["X"])
1
iex> RWC_334.letters(["A", "A", "B"])
8 # "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA"
"""
def permutations([]), do: [[]]
def permutations(char_list),
do: for(char <- char_list, rest <- permutations(char_list -- [char]), do: [char | rest])
def letters(char_list) do
1..length(char_list)
|> Enum.flat_map(fn chunk_len ->
char_list
|> Enum.chunk_every(chunk_len, 1)
|> Enum.flat_map(fn chunk ->
chunk
|> permutations()
|> Enum.map(&Enum.join/1)
end)
end)
|> Enum.uniq()
|> Enum.count()
end
enddefmodule RWC_335 do
@moduledoc """
Given a 2D array, write a function that flips it vertically or horizontally.
iex> array = [
...> [1,2,3],
...> [4,5,6],
...> [7,8,9]
...> ]
iex> RWC_335.flip(array, "horizontal")
[[3,2,1],[6,5,4],[9,8,7]]
iex> RWC_335.flip(array, "vertical")
[[7,8,9],[4,5,6],[1,2,3]]
"""
def flip(lists, "horizontal"),
do:
lists
|> Enum.zip_with(&Function.identity/1)
|> Enum.zip_with(&Enum.reverse/1)
def flip(lists, "vertical"),
do:
lists
|> Enum.zip_with(&Enum.reverse/1)
|> Enum.zip_with(&Function.identity/1)
enddefmodule RWC_360 do
@moduledoc """
Write a function that takes an array of integers representing the number of
flowers planted in a line, and an integer k representing the number of
additional flowers you want to plant. Return whether it's possible to plant
all k flowers without planting any two flowers adjacent to each other.
iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 1], 1)
true # you can plant 1 flower between the others
iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 1], 2)
false
iex> RWC_360.can_plant_flowers([0, 0, 0, 0, 0], 3)
true
iex> RWC_360.can_plant_flowers([1, 0, 1, 0, 1], 1)
false
iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 1, 0, 1], 1)
true
iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 0, 1, 0, 1], 2)
false
iex> RWC_360.can_plant_flowers([1, 0, 0, 0, 0, 0, 1, 0, 1], 2)
true
"""
def can_plant_flowers(flowers, count) do
flowers
|> then(fn flowers ->
flowers
|> pad_ones()
|> Enum.reverse()
|> pad_ones()
|> Enum.reverse()
end)
|> Enum.chunk_by(&(&1 == 1))
|> Enum.filter(&Enum.all?(&1, fn x -> x == 0 end))
|> Enum.map(fn zeros_list ->
zeros_list
|> Enum.chunk_every(3, 2, :discard)
|> Enum.count(&(&1 == [0, 0, 0]))
|> then(&(&1 >= count))
end)
|> Enum.any?(& &1)
end
defp pad_ones(flowers) do
flowers
|> Enum.take(2)
|> case do
[0, 0] ->
[0 | flowers]
_ ->
flowers
end
end
enddefmodule RWC_361 do
@moduledoc """
Given an integer array nums, return the length of the longest
increasing subsequence.
iex> RWC_361.increasing_subsequence([10, 9, 2, 3, 7, 101, 18])
4
iex> RWC_361.increasing_subsequence([4, 4, 4, 4, 3])
1
"""
def increasing_subsequence(input) do
input
|> Enum.chunk_every(2, 1, :discard)
|> Enum.map(fn [a, b] -> a < b end)
|> Enum.chunk_by(& &1)
|> Enum.flat_map(fn
[true | _] = sub -> [length(sub)]
_ -> []
end)
|> Enum.max(&>=/2, fn -> 0 end)
|> then(&(&1 + 1))
end
enddefmodule RWC_364 do
@moduledoc """
Create a function that should take one argument n, which is a
positive integer. The function should return the sum of all
squared positive integers between 1 and n, inclusive.
iex> RWC_364.squares(5)
55
iex> RWC_364.squares(10)
385
iex> RWC_364.squares(25)
5525
iex> RWC_364.squares(100)
338350
"""
def squares(num, sum \\ 0)
def squares(0, sum), do: sum
def squares(num, sum), do: squares(num - 1, sum + num * num)
end👀
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