311. Sparse Matrix Multiplication

class Solution {
    public int[][] multiply(int[][] A, int[][] B) {
      int m = A.length;
      int n = A[0].length;
      int nB = B[0].length;
      int[][] C = new int[m][nB];
      
      for(int  i = 0; i < m; i++){
        for(int k = 0; k < n; k++){
          if(A[i][k] != 0){
            for(int j = 0; j< nB; j++){
              if(B[k][j] != 0){
                C[i][j] += A[i][k] * B[k][j];
              }
            }
          }
        }
      }
      return C;
    }
}