leetcode weekly 132 to 136 - other problems

1074. Number of Submatrices That Sum to Target

Submatrices Sum.

// CY first attempt (5728 ms, 48.58%, 13 MB, 100%)
int numSubmatrixSumTarget(vector<vector<int>>& matrix, int target) {
  const int m = matrix.size(), n = matrix[0].size();
  vector<int> prefSum(m + 1);
  vector<int> rowSum(m);
  
  int total = 0;
  for (int i = 0; i < n; ++i) {
    fill(rowSum.begin(), rowSum.end(), 0);

    for (int j = i; j < n; ++j) {
      for (int k = 0; k < m; ++k)
        rowSum[k] += matrix[k][j];

      for (int k = 1; k <= m; ++k)
        prefSum[k] = prefSum[k - 1] + rowSum[k - 1];
        
      for (int k1 = 0; k1 < m; ++k1)
        for (int k2 = k1 + 1; k2 <= m; ++k2)
          if (prefSum[k2] - prefSum[k1] == target)
            ++total;
    }
  }
  
  return total;
}