268. Missing Number

 1 static int wing=[]()
 2 {
 3     std::ios::sync_with_stdio(false);
 4     cin.tie(NULL);
 5     return 0;
 6 }();
 7 
 8 class Solution 
 9 {
10 public:
11     int missingNumber(vector<int>& nums) 
12     {
13         int sum=0;
14         int count=nums.size();
15         int osum=(count*(count+1))>>1;
16         for(int i:nums)
17             sum+=i;
18         return osum-sum;
19     }
20 };