[LeetCode] 268

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?

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