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

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        if(nums.size() == 0) return 0;
        
        int sumOrigin = 0, sumCurrent = 0;
        for(int i = 0; i < nums.size(); i++){
            sumCurrent += nums[i];
            sumOrigin += i + 1;
        }
        return sumOrigin - sumCurrent;
    }
};