Given a non-empty 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?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

Solution:

class Solution {
    public int singleNumber(int[] nums) {
        int a=0;
        if(nums==null) return 0;
        for(int i:nums){
            a^=i;
        }
        return a;
    }
}

Time:O(n)
Space:O(1)

0异或100=100
100异或100=0
只出现一次，最后异或剩下的就是所求了