leetcode 442. Find All Duplicates in an Array

Given an integer array nums of length n where all the integers of nums are in the range [1, n] and each integer appears once or twice, return an array of all the integers that appears twice.

You must write an algorithm that runs in O(n) time and uses only constant extra space.

Example 1:

Input: nums = [4,3,2,7,8,2,3,1]Output: [2,3]

Example 2:

Input: nums = [1,1,2]Output: [1]

Example 3:

Input: nums = [1]Output: []

Constraints:

• n == nums.length

• 1 <= n <= 105

• 1 <= nums[i] <= n

• Each element in nums appears once or twice.

Success

Details 

Runtime: 39 ms, faster than 10.65% of Java online submissions for Find All Duplicates in an Array.

Memory Usage: 68.4 MB, less than 18.64% of Java online submissions for Find All Duplicates in an Array.