_311.java

package com.fishercoder.solutions;

/**
 * 311. 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 |

 */
public class _311 {

    public static class Solution1 {
        public int[][] multiply(int[][] A, int[][] B) {
            int m = A.length;
            int n = A[0].length;
            int p = B[0].length;
            int[][] C = new int[m][p];
            for (int i = 0; i < m; i++) {
                for (int j = 0; j < n; j++) {
                    if (A[i][j] != 0) {
                        for (int k = 0; k < p; k++) {
                            if (B[j][k] != 0) {
                                C[i][k] += A[i][j] * B[j][k];
                            }
                        }
                    }
                }
            }
            return C;
        }
    }
}