[LeetCode] Filter Elements from Array

17 Apr 2024 in Development on Algorithm

• PROBLEMS
  • Description
  • Example
  • Constraints
  • Solution
  • Retrospect

PROBLEMS

Description

---

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

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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

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

Solution

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• Runtime: 55ms
• Memory: 51.05MB

/**
 * @param {number[]} arr
 * @param {Function} fn
 * @return {number[]}
 */
var filter = function(arr, fn) {
    return arr.reduce((acc, cur, idx) => fn(cur, idx) ? [...acc,cur] : acc, [])
};

Retrospect

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전에 풀었던 유형과 문제가 비슷하다고 생각했다. 파라미터로 받는 함수에 의해 참 거짓이 판별되고 true일때마다 값을 계속 누적해나갔다. filter를 사용하면 편하게 풀었을꺼 같지만 문제에서 사용하지 말라고 했기 때문에 reduce를 사용하였다.