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[leetcode] problem 442 – find all duplicates in an array

admin 11月 13, 2020 0

Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O(n) runtime?

Example

Input:
[4,3,2,7,8,2,3,1]

Output:
[2,3]

Code

public List<Integer> (int[] nums) {
    List<Integer> result = new ArrayList<>();

    for (int i = 0; i < nums.length; i++) {
        int idx = Math.abs(nums[i]) - 1;

        if (nums[idx] < 0)
            result.add(Math.abs(nums[i]));
        else
            nums[idx] *= -1;
    }

    return result;
}