Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.app
Find all the elements that appear twice in this array.this
Could you do it without extra space and in O(n) runtime?spa
Example:
Input:
[4,3,2,7,8,2,3,1]code
Output:
[2,3]element
class Solution { public List<Integer> findDuplicates(int[] nums) { //use index to record visited: times -1 List<Integer> res = new ArrayList<>(); for (int i = 0; i < nums.length; i++) { int index = nums[i] > 0 ? nums[i]-1 : -nums[i]-1; if (nums[index] < 0) res.add(index+1); nums[index] *= -1; } return res; } }