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?

进行一次扫描，把所有数据异或在一起，最终结果就是所求结果。

    int singleNumber(int A[], int n) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int result = 0;
        int i;
        for(i = 0; i < n; i++){
            result ^= A[i];
        }
        return result;
    }