# Finding the perimeter of a river

## Question

Suppose you're given a matrix of `1s`

and `0s`

that represents a map of rivers. You can assume that the grid cells in your map are only connected horizontally and vertically (e.g. no diagonal connections). You can assume that `1`

represents water (your river) and `0`

represents land/your river bank. Each cell has a length of `1`

and is square in your map. Given this, write code to determine the perimeter of your river.

Examples:

```
Input: [[1,0]]
Output: 4
Input: [[1,0,1],
[1,1,1]]
Output: 12
```