LeetCode - Sparse Matrix Multiplication

SparseMatrixMultiplication.java

// 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 |


 public int[][] multiply(int[][] A, int[][] B) {
    int ma = A.length, na = A[0].length, nb = B[0].length;
    int[][] res = new int[ma][nb];
    for(int i = 0; i < ma; i++){
        for(int j = 0; j < na; j++){
            if(A[i][j] == 0) continue; 
            for(int k = 0; k < nb; k++){
                res[i][k] += A[i][j] * B[j][k];
            }
        }
    }
    return res;
}