136. Single Number

136. Single Number
     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
python

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        res = 0
        for i in nums:
            res = res^i
        return res

java:

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

& : 按位与操作, 只有 1&1 为 1, 其它情况为 0. 可用于进位运算
| : 按位或操作 , 只有 0|0 为0 ,其他情况为1
~ : 逐位取反
^ : 异或, 相同为 0 ,相异为 1 . 可用于加操作 (不包括进位项 )
<< : 左移操作, 2的幂有关 >> : 右移操作, 2的幂有关
交换律：a ^ b ^ c <=> a ^ c ^ b
任何数于0异或为任何数 0 ^ n =n
相同的数异或为0: n ^ n = 0
两个数相同就会为0