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137. Single Number II

Difficulty Topics

Description

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.

Solution

single-number-ii.py
class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        ones = twos = 0

        for x in nums:
            ones = (ones ^ x) & ~twos
            twos = (twos ^ x) & ~ones

        return ones