LeetCode in Kotlin

2634. Filter Elements from Array

Easy

Given an integer array arr and a filtering function fn, return a filtered array filteredArr.

The fn function takes one or two arguments:

• arr[i] - number from the arr
• i - index of arr[i]

filteredArr should only contain the elements from the arr for which the expression fn(arr[i], i) evaluates to a truthy value. A truthy value is a value where Boolean(value) returns true.

Please solve it without the built-in Array.filter method.

Example 1:

Input: arr = [0,10,20,30], fn = function greaterThan10(n) { return n > 10; }

Output: [20,30]

Explanation:

const newArray = filter(arr, fn); // [20, 30]

The function filters out values that are not greater than 10

Example 2:

Input: arr = [1,2,3], fn = function firstIndex(n, i) { return i === 0; }

Output: [1]

Explanation:

fn can also accept the index of each element

In this case, the function removes elements not at index 0

Example 3:

Input: arr = [-2,-1,0,1,2], fn = function plusOne(n) { return n + 1 }

Output: [-2,0,1,2]

Explanation: Falsey values such as 0 should be filtered out

Constraints:

• 0 <= arr.length <= 1000
• -109 <= arr[i] <= 109

Solution

function filter(arr: number[], fn: (n: number, i: number) => boolean): number[] {
    const filteredArr: number[] = []

    for (let i = 0; i < arr.length; i++) {
        if (fn(arr[i], i)) filteredArr.push(arr[i])
    }

    return filteredArr
}

export { filter }

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