LeetCode: Check If N and Its Double Exist Solution

Approach

Nested loop: for every element, check with other elements

Hash table: save a loop by using a hash table of the checked elements

Implementation (nested loop)

1/**
2 * @param {number[]} arr
3 * @return {boolean}
4 */
5var checkIfExist = function (arr) {
6  let existed = false
7
8  for (let i = 0; i < arr.length; i++) {
9    for (let j = 0; j < arr.length; j++) {
10      if (i !== j && (arr[i] === 2 * arr[j] || arr[j] === 2 * arr[i])) {
11        existed = true
12      }
13    }
14  }
15
16  return existed
17}

Implementation (hash table)

1/**
2 * @param {number[]} arr
3 * @return {boolean}
4 */
5var checkIfExist = function (arr) {
6  const iterated = new Set()
7  let existed = false
8
9  for (const num of arr) {
10    if (iterated.has(num * 2) || iterated.has(num / 2)) {
11      existed = true
12    }
13    iterated.add(num)
14  }
15
16  return existed
17}