Single Number II

Given an integer array nums where every element appears three times except for one, which appears exactly once. Find the single element that appears only once. Implement a solution with linear runtime complexity and use only constant extra space.

Constraints

• 1 <= nums.length <= 3 * 10^4
• -2^31 <= nums[i] <= 2^31 - 1
• Each element in nums appears exactly three times except for one element which appears once.