218. Find All Duplicates in an Array
Medium
Index Sign Marking
Array
Problem
Given an integer array nums of length n where each value is between 1 and n and each value appears once or twice, return all values that appear twice.
Examples
Example 1
Input: [4,3,2,7,8,2,3,1]
Output: [2,3]
Example 2
Input: [1,1,2]
Output: [1]
Example 3
Input: [1]
Output: []
Constraints
� 1 <= nums.length <= 100000
� 1 <= nums[i] <= nums.length
� Each value appears once or twice.
Hints
?? Use abs(nums[i]) - 1 as an index.
?? A previously marked index reveals a duplicate.
Expected Complexity
Time: O(n)
Space: O(1) auxiliary
Follow-up
Can you solve it in O(n) time with O(1) auxiliary space?
Practice Notes
Attempts: 0
Time spent: 0min
Hints used: 0
JavaScript
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Case 1
Case 2
Case 3
Input
[4,3,2,7,8,2,3,1]Expected
[2,3]