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: Input: A = [
[ 1, 0, 0],
[-1, 0, 3]
] B = [
[ 7, 0, 0 ],
[ 0, 0, 0 ],
[ 0, 0, 1 ]
] Output: | 1 0 0 | | 7 0 0 | | 7 0 0 |
AB = | -1 0 3 | x | 0 0 0 | = | -7 0 3 |
| 0 0 1 |