English
442. Find All Duplicates in an Array
Problem Statement:
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.
Solution:
java
public List<Integer> findDuplicates(int[] nums) {
ArrayList<Integer> list = new ArrayList<>();
for (int i = 0; i < nums.length; i++) {
int n = Math.abs(nums[i]);
if (nums[n - 1] < 0)
list.add(n);
else
nums[n - 1] = -nums[n - 1];
}
return list;
}
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