Missing Number

题目：

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?

解析：

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        for(int i = 0; i <= nums.size(); i++)
            if(nums[i] != i)
                return i;
    }
};

高效的算法应该是使用位运算，我没明白，也不想深究：

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int result = 0;
        for (int i = 0; i < nums.size(); i++)
            result ^= nums[i]^(i+1);
        return result;
    }
};