开始刷leetcode day31：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?

Java:

 public static int singleNumber(int[] A) {
int x = 0;
for (int a : A) {
x = x ^ a;
}
return x;
}