Sparse Matrix Multiplication

Given two sparse matrices A and B, return the result of AB.

You may assume that A's column number is equal to B's row number.

Example:

A = [ [ 1, 0, 0], [-1, 0, 3] ]

B = [ [ 7, 0, 0 ], [ 0, 0, 0 ], [ 0, 0, 1 ] ]

 |  1 0 0 |   | 7 0 0 |   |  7 0 0 |

AB = | -1 0 3 | x | 0 0 0 | = | -7 0 3 | | 0 0 1 |

Solution

public class Solution {
      public int[][] multiply(int[][] A, int[][] B) {
        int row1 = A.length;
        int col1 = A[0].length;
        int row2 = B.length;
        int col2 = B[0].length;

        int[][] result = new int[row1][col2];
        for (int i = 0; i < row1; i++) {
            for (int j = 0; j < col1; j++) {
                if (A[i][j] != 0) {

                    for (int k = 0; k < col2; k++) {
                        if (B[j][k] != 0) {
                            result[i][k] += A[i][j] * B[j][k];
                        }
                    }

                }
            }
        }

        return result;
    }
}