Problem statement

https://binarysearch.com/problems/Lone-Integer/

Solution

Equal to Leetcode 0137. Single Number II

Complexity

It is O(n) for time and O(1) for space.

Code

class Solution:
    def solve(self, nums):
        ones, twos = 0, 0
        for x in nums:
            ones = (ones ^ x) & ~twos
            twos = (twos ^ x) & ~ones
        return ones