leetcode 268. Missing Number

Given an array containing n distinct numbers taken from

0, 1, 2, ..., n

, find the one that is missing from the array.

For example,
Given nums =

[0, 1, 3]

return

2

.

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

呵呵

class Solution {
public:
int missingNumber(vector<int>& nums) {
int sum = 0;
for (int x : nums) {
sum += x;
}
int n = nums.size();
return  n * (1 + n) / 2 - sum;
}
};