Problem

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

Example

Input: [3,0,1]
Output: 2

Input: [9,6,4,2,3,5,7,0,1]
Output: 8

Code

static int var = [](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();
class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int size = nums.size();
        int sum = (size+1)*size/2;
        for(int i=0;i<size;i++){
            sum -= nums[i];
        }
        return sum;
    }
};

Result

268. Missing Number.png