LeetCode刷题笔录 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?

用hashmap count是第一想法。

不用extra memory的话，用XOR可以做。m^m = 0. 0^n = n。所以把数组所有元素XOR一遍就行了。

public class Solution {
public int singleNumber(int[] A) {
int result = A[0];
for(int i = 1; i < A.length; i++){
result ^= A[i];
}
return result;
}
}