268.Missing Number

    int missingNumber(vector<int>& nums) {
        int total = nums.size()*(nums.size()+1)/2;
        int sum=0;
        for(auto num : nums){
            sum+=num;
        }
        return total - sum; 
    }

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

• http://www.cnblogs.com/grandyang/p/4756677.html