LeetCode Solutions

137. Single Number II

Time: $O(32n) = O(n)$

Space: $O(1)$

			

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;
  }
};
			

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;
  }
}
			

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