Algorithm
30 Days of JavaScript
Filter Elements from Array

2634. Filter Elements from Array

Tags

  • Basic Array Transformations

Link

https://leetcode.com/problems/filter-elements-from-array/description/?envType=study-plan-v2&envId=30-days-of-javascript (opens in a new tab)

Question

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

Answer

JavaScript

/**
 * @param {number[]} arr
 * @param {Function} fn
 * @return {number[]}
 */
var filter = function (arr, fn) {
  const newArr = [];
  arr.forEach((arr, i) => {
    if (fn(arr, i)) newArr.push(arr);
  });
  return newArr;
};
/**
 * @param {number[]} arr
 * @param {Function} fn
 * @return {number[]}
 */
var filter = function (arr, fn) {
  let retArray = [];
  for (let i = 0; i < arr.length; i++) {
    if (fn(arr[i], i)) {
      retArray.push(arr[i]);
    }
  }
  return retArray;
};
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