 # davearonson's solution

## to Minesweeper in the Elixir Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Add the numbers to a minesweeper board.

Minesweeper is a popular game where the user has to find the mines using numeric hints that indicate how many mines are directly adjacent (horizontally, vertically, diagonally) to a square.

In this exercise you have to create some code that counts the number of mines adjacent to a square and transforms boards like this (where `*` indicates a mine):

``````+-----+
| * * |
|  *  |
|  *  |
|     |
+-----+
``````

into this:

``````+-----+
|1*3*1|
|13*31|
| 2*2 |
| 111 |
+-----+
``````

## Running tests

Execute the tests with:

``````\$ elixir minesweeper_test.exs
``````

### Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.

For example:

``````# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
``````

Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the test suite.

``````# ExUnit.configure exclude: :pending, trace: true
``````

For more detailed information about the Elixir track, please see the help page.

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### minesweeper_test.exs

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule MinesweeperTest do
use ExUnit.Case

defp clean(b), do: Enum.map(b, &String.replace(&1, ~r/[^*]/, " "))

# @tag :pending
test "zero size board" do
b = []
assert Minesweeper.annotate(clean(b)) == b
end

@tag :pending
test "empty board" do
b = ["   ", "   ", "   "]
assert Minesweeper.annotate(clean(b)) == b
end

@tag :pending
test "board full of mines" do
b = ["***", "***", "***"]
assert Minesweeper.annotate(clean(b)) == b
end

@tag :pending
test "surrounded" do
b = ["***", "*8*", "***"]
assert Minesweeper.annotate(clean(b)) == b
end

@tag :pending
test "horizontal line" do
b = ["1*2*1"]
assert Minesweeper.annotate(clean(b)) == b
end

@tag :pending
test "vertical line" do
b = ["1", "*", "2", "*", "1"]
assert Minesweeper.annotate(clean(b)) == b
end

@tag :pending
test "cross" do
b = [" 2*2 ", "25*52", "*****", "25*52", " 2*2 "]
assert Minesweeper.annotate(clean(b)) == b
end
end``````
``````defmodule Minesweeper do

@doc """
Annotate empty spots next to mines with the number of mines next to them.
"""
@spec annotate([String.t]) :: [String.t]

def annotate(board) do
# make it a *tuple of rows*, with each a tuple of cells
# for each row, for each cell, if it's blank,
# set it to how many neighbors are mines if any.
tuple_version = board
|> Enum.map(&tupleize_string/1)
|> List.to_tuple
board
|> Enum.with_index
|> Enum.map(&(annotate_row(&1, tuple_version)))
end

defp tupleize_string(str) do
str |> String.graphemes |> List.to_tuple
end

defp annotate_row({row, row_num}, board) do
row
|> String.graphemes
|> Enum.with_index
|> Enum.map(&(annotate_cell(&1, row_num, board)))
|> Enum.join
end

defp annotate_cell({"*", col_num}, _row_num, _board), do: "*"
defp annotate_cell({val, col_num},  row_num,  board)  do
count_neighbors(row_num, col_num, board)
|> (fn(x) -> if x == 0, do: " ", else: x end).()
end

defp count_neighbors(row_num, col_num, board) do
(-1..1)
|> Enum.map(&(count_neighbors_in_row(row_num, &1, col_num, board)))
|> Enum.reduce(&+/2)
end

defp count_neighbors_in_row(row_num, row_delta, _col_num, board)
when row_num + row_delta < 0
or row_num + row_delta >= tuple_size(board), do: 0
defp count_neighbors_in_row(row_num, row_delta, col_num, board) do
(-1..1)
|> Enum.map(&(check_neighbors_at(row_delta,
col_num, &1,
elem(board, row_num + row_delta))))
|> Enum.reduce(&+/2)
end

defp check_neighbors_at(0,          _col_num, 0,         _row), do: 0
defp check_neighbors_at(_row_delta,  col_num, col_delta,  row)
when col_num + col_delta < 0
or col_num + col_delta >= tuple_size(row), do: 0
defp check_neighbors_at(_row_delta, col_num, col_delta, row) do
row
|> elem(col_num + col_delta)
|> (fn(x) -> if x == "*", do: 1, else: 0 end).()
end
end``````