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?

 

Runtime: 36ms

 1 class Solution {
 2 public:
 3     int missingNumber(vector<int>& nums) {
 4         if(nums.size() == 0) return 0;
 5         
 6         int sumOrigin = 0, sumCurrent = 0;
 7         for(int i = 0; i < nums.size(); i++){
 8             sumCurrent += nums[i];
 9             sumOrigin += i + 1;
10         }
11         return sumOrigin - sumCurrent;
12     }
13 };