LeetCode 311: Sparse Matrix Multiplication

class Solution {
    public int[][] multiply(int[][] A, int[][] B) {
        if (A.length == 0 || A[0].length == 0 || B.length == 0 || B[0].length == 0 || A[0].length != B.length) {
            return new int[0][0];
        }

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