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?

使用异或或者set来处理。

public class Solution {
    public int singleNumber(int[] nums) {
        if(nums==null||nums.length<=0)
            return 0;
        for(int i=1;i<nums.length;i++)
            nums[0]^=nums[i];
        return nums[0];
    }
}