Single Number II LeetCode Solution | Easy Approach

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 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.

Single Number II Solutions

✅Time: O(32n)=O(n)
✅Space: O(1)

C++

class Solution {
 public:
  int singleNumber(vector<int>& nums) {
    int ans = 0;

    for (int i = 0; i < 32; ++i) {
      int sum = 0;
      for (const int num : nums)
        sum += num >> i & 1;
      sum %= 3;
      ans |= sum << i;
    }

    return ans;
  }
};

Java

 class Solution {
  public int singleNumber(int[] nums) {
    int ans = 0;

    for (int i = 0; i < 32; ++i) {
      int sum = 0;
      for (final int num : nums)
        sum += num >> i & 1;
      sum %= 3;
      ans |= sum << i;
    }

    return ans;
  }
}

 

Python

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

    for num in nums:
      ones ^= num & ~twos
      twos ^= num & ~ones

    return ones

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