[2018-Interview] Single Number

Original question: https://leetcode.com/problems/single-number/description/

Answer: Take use of bitwise XOR, because only when number XOR with itself, result would be 0. Thus, the result of whole array XOR should be that single number

class Solution {
    public int singleNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
            return 0;
        }
        int singleNumber =  0;
        for (int i = 0; i < nums.length ; i ++) {
            singleNumber ^= nums[i];
        }
        return singleNumber;
    }
}