448. Find All Numbers Disappeared in an Array
448. Find All Numbers Disappeared in an Array
Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others
appear once.
Find all the elements of [1, n] inclusive that do not appear in this array.
Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as
extra space.
Example:
Input:
[4,3,2,7,8,2,3,1]
Output:
[5,6]
- negative as duplicate
public List<Integer> findDisappearedNumbers(int[] nums) {
for(int i = 0; i < nums.length; i++) {
int j = Math.abs(nums[i])-1;
if(nums[j] > 0)
nums[j] = -nums[j];
}
ArrayList<Integer> result = new ArrayList<>();
for(int i = 0; i < nums.length; i++) {
if(nums[i] > 0)
result.add(i+1);
}
return result;
}