137. Single Number II

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Problem

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:

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

Code

class Solution {
    public int singleNumber(int[] nums) {
        int ones = 0;
        int twos = 0;
        for(int i = 0; i < nums.length; i++){
            ones = (ones ^ nums[i]) & ~twos;
            twos = (twos ^ nums[i]) & ~ones;
        }

        return ones;
    }
}