public class Solution
extends Object
137 - Single Number II\.
Medium
Given an integer array `nums` where every element appears **three times** except for one, which appears **exactly once**. _Find the single element and return it_.
You must implement a solution with a linear runtime complexity and use only constant extra space.
**Example 1:**
**Input:** nums = [2,2,3,2]
**Output:** 3
**Example 2:**
**Input:** nums = [0,1,0,1,0,1,99]
**Output:** 99
**Constraints:**
* 1 <= nums.length <= 3 * 104
* -231 <= nums[i] <= 231 - 1
* Each element in `nums` appears exactly **three times** except for one element which appears **once**.