来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/single-number

1. TITLE

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

2. JAVA Answer

Time Complexity:O(N),Space Complexity:O(1)

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