River Crossing
Moderate
English

' River crossing puzzle ' is the famous classic puzzle. (also known as Wolf, goat and cabbage problem )

 summary: The farmer needs to carry wolf, goat and cabbage by boat across the river. Only one can be loaded on the boat at a time. Don't leave wolf and goat on the bank (wolf eats goat). Don't leave goat and cabbage on the bank (goat eats cabbage).

This time, I will extend this puzzle a little. The number of wolves, goat, cabbages and payload is arbitrary.
(see precondition)

You are given four integers as the number of wolves, goats, cabbages and payload of the boat. You have to return the minimum number of boat crossings required to carry all the loads. (If not possible, return None.)

NOTE:

• All loads can live together on the boat.

Example:

```river_crossing(1, 1, 1, 1) == 7  # original
river_crossing(1, 1, 1, 2) == 3  # payload +1
river_crossing(2, 1, 1, 2) == 5  # payload +1, wolf +1
river_crossing(1, 2, 1, 1) is None  # impossible```

Input: The number of wolves, goats, cabbages and payload (4 integers).

Output: The minimum number of the boat crossings (an integer).

Precondition:

• 1 ≤ wolves + goats + cabbages ≤ 10
• 1 ≤ payload ≤ 5

## Become Awesome

• No Limits
• More Content
Settings
Code:
Other:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

`pip3 install checkio_client`

`checkio --domain=py config --key=`

Sync solutions into your local folder

`checkio sync`

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

`checkio serv -d`

Alternatevly, you can install Chrome extension or FF addon

`checkio install-plugin`
`checkio install-plugin --ff`
`checkio install-plugin --chromium`

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.