LeetCode - Single Number

Question：

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?

两个相同的数字异或的结果是0.

代码如下：

public int singleNumber(int[] A) {
        int single = 0;
		int length = A.length;
		if (length == 0) {
			return -1;
			
		}
		
		for (int i = 0; i < length; i++) {
			single ^= A[i];  
		}
		
		return single;
    }