leetcode 136 Single Number bit Option

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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:

the method is xor option, principles is  : 0 xor 0 = 0; 0 xor 1 = 1；any  num xor itself  =  0,so we pass the array and xor its elements all,so the result  which is we want.

ac code follow: 

1 class solution {
2 public:
3     int singlenumber(vector<int>& nums) {
4         int res = nums[0];
5         for(int i = 1;i < nums.size();++i)
6             res = nums[i]^res;
7         return res;
8     }
9 };