Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.
Example 1
Input: [3,0,1]
Output: 2
Example 2
Input: [9,6,4,2,3,5,7,0,1]
Output: 8 用异或的办法：
class Solution {
public:
int missingNumber(vector<int>& nums) {
int len = nums.size();
if(len == )
return ;
int x = ;
for (int i=;i<=len;i++)
x ^= i;
for (int i=;i<len;i++)
x ^= nums[i];
return x;
}
};