[leetcode] Single Number

From : https://leetcode.com/problems/single-number/

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

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