[leetcode][*] 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?

Attention:

 XOR in C++ should be ^

 int singleNumber(int A[], int n) {

        if(n == 0) return 0;

        int ret = A[0];

        for(int i = 1; i < n; ++i)

            ret = ret ^ A[i];

        return ret;

    }