[LintCode] 寻找缺失的数

 class Solution {
 public:
     /**
      * @param nums: a vector of integers
      * @return: an integer
      */
     int findMissing(vector<int> &nums) {
         // write your code here
         int n = nums.size();
         int number = ;
         for (int i = ; i <= n; i++)
             number ^= i;
         for (int i = ; i < n; i++)
             number ^= nums[i];
         return number;
     }
 };