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:

```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 |
```

Constraints:

• `1 <= A.length, B.length <= 100`
• `1 <= A[i].length, B[i].length <= 100`
• `-100 <= A[i][j], B[i][j] <= 100`

311. Sparse Matrix Multiplication
``````struct Solution;

impl Solution {
fn multiply(a: Vec<Vec<i32>>, b: Vec<Vec<i32>>) -> Vec<Vec<i32>> {
let l = a.len();
let m = b.len();
let n = b[0].len();
let mut res = vec![vec![0; n]; l];
for i in 0..l {
for j in 0..n {
for k in 0..m {
res[i][j] += a[i][k] * b[k][j];
}
}
}
res
}
}

#[test]
fn test() {
let a = vec_vec_i32![[1, 0, 0], [-1, 0, 3]];
let b = vec_vec_i32![[7, 0, 0], [0, 0, 0], [0, 0, 1]];
let res = vec_vec_i32![[7, 0, 0], [-7, 0, 3]];
assert_eq!(Solution::multiply(a, b), res);
}
``````