Sparse Matrix Multiplication

Sparse Matrix Multiplication hash table

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 |

Sparse Matrix Multiplication Solution

public class SparseMatrixMultiplication {
    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 j = 0; j < n; j++) {
                if(A[i][j] != 0) {
                    for(int k = 0; k < nB; k++) {
                        if(B[j][k] != 0) {
                            C[i][k] += A[i][j] * B[j][k];
                        }
                    }
                }
            }
        }

        return C;
    }
}

Last modified October 4, 2020