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 rowsA = A.length; int rowsB = B.length; if (rowsA==0 || rowsB==0 || B[0].length==0) return new int[0][0]; int colsB = B[0].length; int colsA = rowsB; int[][] res = new int[rowsA][colsB]; for (int i=0;i<rowsA;i++) for (int j=0;j<colsA;j++) if (A[i][j]!=0){ for (int k=0;k<colsB;k++) if (B[j][k]!=0){ res[i][k] += A[i][j] * B[j][k]; } } return res; } }