Medium
Quiz
#442 Find All Duplicates in an Array
APPROACH
An integer array nums of length n has every element in the range [1, n], and each element appears exactly once or twice. Find all elements that occur exactly twice and return them in any order.
Constraints: O(n) time and O(1) extra space (not counting the output array).
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: []
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What is the optimal approach for this problem?