2634. Filter Elements from Array

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# 題目敘述

Given an integer array arr and a filtering function fn , return a new array with a fewer or equal number of elements.

The returned array should only contain elements where fn(arr[i], i) evaluated to a truthy value.

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

# 解題思路

# Solution

/**

 * @param {number[]} arr

 * @param {Function} fn

 * @return {number[]}

 */

var filter = function(arr, fn) {

    let ans = [];

    for (let i=0; i<arr.length; i++) {

        if (fn(arr[i], i)){

            ans.push(arr[i]);

        }

    }

    return ans;

};

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

    const ans: number[] = [];

    for (let i = 0; i < arr.length; i++) {

        if (fn(arr[i], i)){

            ans.push(arr[i]);

        }

    }

    return ans;

};