# 448.Find All Numbers Disappeared in an Array

**448.Find All Numbers Disappeared in an Array**

难度:Easy

> 给定一个范围在 1 ≤ a\[i] ≤ n ( n = 数组大小 ) 的 整型数组，数组中的元素一些出现了两次，另一些只出现一次。

找到所有在 \[1, n] 范围之间没有出现在数组中的数字。

您能在不使用额外空间且时间复杂度为O(n)的情况下完成这个任务吗? 你可以假定返回的数组不算在额外空间内。

示例:

输入: \[4,3,2,7,8,2,3,1]

输出: \[5,6]

利用数组下标计算，当存在时将该索引值变为负数，这样不影响后面的索引判断。

```
class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        vector<int >res;
        int tmp=-1;
        for(int i=0;i<nums.size();i++)
        {
            nums[abs(nums[i])-1]=-abs(nums[abs(nums[i])-1]);
        }
        for(int i=0;i<nums.size();i++)
            if(nums[i]>0) res.push_back(i+1);
        return res;
            
    }
};
```

> 执行用时 : 132 ms, 在Find All Numbers Disappeared in an Array的C++提交中击败了97.49% 的用户\
> 内存消耗 : 14.8 MB, 在Find All Numbers Disappeared in an Array的C++提交中击败了82.07% 的用户


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