https://leetcode.com/problems/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

Example:

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

Output:
[5,6]

代碼：

class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        int n = nums.size();
        int vis[100000] = {0};
        for(int i = 0; i < n; i ++) {
            vis[nums[i]] ++;
        }
        vector<int> ans;
        for(int i = 1; i <= n; i ++) {
            if(!vis[i]) ans.push_back(i);
        }
        return ans;
    }
};

#Leetcode# 448. Find All Numbers Disappeared in an Array