LeetCode: Find All Numbers Disappeared in an Array Solution

Hash table to check existing

Approach

Use hash table (Set) as existing reference

Implementation

1/**
2 * @param {number[]} nums
3 * @return {number[]}
4 */
5var findDisappearedNumbers = function (nums) {
6 const set = new Set(nums)
7 const res = []
8
9 for (let num = 1; num <= nums.length; num++) {
10 if (set.has(num) === false) {
11 res.push(num)
12 }
13 }
14
15 return res
16}

O(1) memory approach

Different existence marking strategy:

  • use index-based to mark the existence of a number (eg. for number 4 to exist, use index 3 to mark)
  • transfrom
    nums
    array to existence checking array
  • if a number is existed, the array value at its index-based will be negative
1For array
2[4, 3, 2, 7, 8, 2, 3, 1]
3
4Transformation
5[ 4, 3, 2, -7, 8, 2, 3, 1]
6[ 4, 3, -2, -7, 8, 2, 3, 1]
7[ 4, -3, -2, -7, 8, 2, 3, 1]
8[ 4, -3, -2, -7, 8, 2, -3, 1]
9[ 4, -3, -2, -7, 8, 2, -3, -1]
10[ 4, -3, -2, -7, 8, 2, -3, -1]
11[ 4, -3, -2, -7, 8, 2, -3, -1]
12[-4, -3, -2, -7, 8, 2, -3, -1]

Implementation

1/**
2 * @param {number[]} nums
3 * @return {number[]}
4 */
5var findDisappearedNumbers = function (nums) {
6 for (const num of nums) {
7 const i = Math.abs(num) - 1
8 nums[i] = -Math.abs(nums[i])
9 // console.log(nums) // use this to see how things work
10 }
11
12 return nums.map((num, i) => (num < 0 ? 0 : i + 1)).filter(Boolean)
13}

Comments

Loading comments...

Tags

leetcode

array

hash table

Apply and earn a $2,500 bonus once you're hired on your first job!

Clients from the Fortune 500 to Silicon Valley startups

Choose your own rate, get paid on time

From hourly, part-time, to full-time positions

Flexible remote working environment

A lot of open JavaScript jobs!!

Fact corner: Referred talent are 5x more likely to pass the Toptal screening process than the average applicant.

Still hesitate? Read HoningJS author's guide on dealing with Toptal interview process.

Next Post

LeetCode: Third Maximum Number

Aug 3, 2021

Sort unique numbers

Previous Post

LeetCode: Sort Array By Parity

Jul 27, 2021

Filter and concat

HoningJS

Search Posts