249. Find All Duplicates in an Array
MediumArray
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 auxiliary space (not counting the space needed to store the output).
Examples
Input: [4,3,2,7,8,2,3,1]
Output: [2,3]
Explanation: 2 and 3 each appear twice.
Constraints
- n == nums.length
- 1 <= n <= 10^5
- 1 <= nums[i] <= n
- Each element appears once or twice.
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