# Sequence

**by [Matt Hall](https://github.com/kwinkunks)**

You have a string of lithology codes, reading from the **bottom up** of a geological section. There is a sample every metre. There are three lithologies:

- **M**udstone
- **F**ine sandstone or siltstone
- **S**andstone

The strings look like this:

      ...MFFSSFSSSS...

Your data, when you receive it, will be much longer than this.

We need to get some geological information from this string of codes. Specifically, you need to answer 3 questions:

1. What is the total thickess in metres of sandstone (`S`)? Each sample represents one metre.
2. How many sandstone beds are there? A bed is a contiguous group of one lithology, so `MMFFF` is 2 beds, one of `M` and one of `F`.
3. How many times does the most common *upwards* bed transition occur? Do not include transitions from a lithology to itself.

Remember that the sequence is given to you from the bottom up. So an upwards transition is equivalent to a transition from left to right.


## Example

Here is some example input:

      SSMMFFFFFFFFSSMFFSSFSSSSFMFSSSSFFSSFFFMMS
      ^^          ^^   ^^ ^^^^   ^^^^  ^^     ^

And the answers to the 3 questions:

- In this example, the total thickess of sandstone is 17 m. So the required answer is: **17**
- There are 7 sandstone beds in the sequence (marked above). The answer is: **7**
- The most common bed transition is `F` to `S`, which occurs 5 times. So the answer is: **5**


## A quick reminder how this works

This document is formatted in [Markdown](https://daringfireball.net/projects/markdown/).

You can retrieve your data, which is always a string, by choosing a **`<KEY>`** (also a string). This ensures that you have different data from other people, so be creative. 

```
url = 'https://kata.scienxlab.org/challenge/sequence'
params = {
    'key': <KEY>  # Replace <KEY> with your own string.
}
r = requests.get(url, params)
r.text
```

To answer question 1, change the `params`:

```
params = {
    'key': <KEY>,   # Use the same key you used to get your input.
    'question': 1,
    'answer': 1234  # Your answer; can be a float, int, list or array;
                    # the challenge description will tell you which.
}
```

To get a hint for a question, provide the question number but no answer:

```
params = {
    'question': 1,
}
```

[Complete instructions at kata.scienxlab.org](https://kata.scienxlab.org/challenge)

[An example notebook to get you started](https://gist.github.com/kwinkunks/50f11dac6ab7ff8c3e6c7b34536501a2)

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