Given a non-empty array of integers, every element appears twice except for one. Find that single one.
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
Input: [2,2,1] Output: 1
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.
To see more hashtable related problems, see
Problems and Solutions of Hashmap.