Source: https://leetcode.com/problems/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

We can simply use hashmap to count every number’s count of appearing, then output the numbers only occur once.

the Code:

Github: https://github.com/tinyfool/leetcode/tree/master/src/p0136

To see more hashtable related problems, see

Problems and Solutions of Hashmap.