# Question

Formatted question description: https://leetcode.ca/all/311.html

 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 |



# Algorithm

Make sure that A[i][k] is not 0 before continuing to calculate, and then traverse the kth row of matrix B. If B[K][J] is not 0, accumulate the result matrix res[i][j] += A[i][k] * B[k][j], so that we can efficiently calculate the multiplication of the sparse matrix.

Java