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;
  }
};