Problem

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

Solution

Using “XOR” operation is the most efficient way to solve this problem.

Example 2:

Input: [4,1,2,1,2]
Output: 4

Checkout following picture which shows the procedure of processing the example:

Code

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

Detail
Execution time :1 ms, beat 99.53% Java commit
Memory Used :38.9 MB, beat 33.39% Java commit