136. Single Number

Given a non-empty array of integers, every element appears twice except for one. Find that single one.

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

class Solution {
    public int singleNumber(int[] nums) {
    //hashset
    Set<Integer> set=new HashSet<>();
    for(int i=0;i<nums.length;i++){
        if(!set.add(nums[i])){
            set.remove(nums[i]);
        }
    }
    return set.iterator().next();
    }
}