# 0448. Find All Numbers Disappeared in an Array
###### tags: `Leetcode` `Easy` `Indexing Sort`
Link: https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/description/
## 思路 $O(N)$ $O(1)$
和[0442. Find All Duplicates in an Array](https://hackmd.io/UnpI8ph4Q6icK2K1UxDHfg)差不多
通过swap使得```nums[i]==i+1```
如果不等于那么说明```i+1```不存在
## Code

class Solution {
    public List<Integer> findDisappearedNumbers(int[] nums) {
        List<Integer> ans = new ArrayList<>();
        int n = nums.length;
        for(int i=0; i<n; i++){
            if(nums[i]!=i+1){
                while(nums[nums[i]-1]!=nums[i]){
                    swap(nums, i, nums[i]-1);
                }
            }
        }
        for(int i=0; i<n; i++){
            if(nums[i]!=i+1) ans.add(i+1);
        }
        return ans;
    }
    private void swap(int[] nums, int idx1, int idx2){
        int temp = nums[idx1];
        nums[idx1] = nums[idx2];
        nums[idx2] = temp;
    }
}