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

/*Time: O(n), Space: O(1)
exclusive or operation:
1 XOR 1 = 0
1 XOR 0 = 1
0 XOR 1 = 1
0 XOR 0 = 0
0 XOR A = A  关键：0异或任何数还是任何数
*/
public int singleNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
            return 0;
        }
        
        int result = 0;
        
        for (int i = 0; i < nums.length; i++) {
            result = result ^ nums[i];
        }
        
        return result;
    }