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?

Credits:

一串连续的数，找到缺的那个

C++（22ms）：

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

C++(26ms):

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