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michaelkpfeifer's solution

to Minesweeper in the Elixir Track

Published at Aug 09 2020 · 0 comments
Instructions
Test suite
Solution

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:

``````\$ mix test
``````

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
``````

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

Submitting Incomplete Solutions

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

minesweeper_test.exs

``````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``````

test_helper.exs

``````ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)``````
``````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([]) do
[]
end

def annotate(board) do
nr_rows = length(board)
nr_cols = String.length(Enum.at(board, 0))
source = board_to_map(board)

Enum.reduce(
for r <- 0..(nr_rows - 1), c <- 0..(nr_cols - 1) do
{r, c}
end,
source,
fn {r, c}, acc ->
put_in(acc, [r, c], sum_for_coordinate(r, c, nr_rows, nr_cols, source))
end
)
|> Map.values()
|> Enum.map(fn row -> Map.values(row) |> Enum.join() end)
end

def board_to_map(board) do
Enum.map(board, fn row -> row_to_map(row) end)
|> Enum.with_index()
|> Enum.reduce(%{}, fn {row, index}, map -> Map.put_new(map, index, row) end)
end

def row_to_map(row) do
String.graphemes(row)
|> Enum.with_index()
|> Enum.reduce(%{}, fn {char, index}, map -> Map.put_new(map, index, char) end)
end

def coordinate_list(row, column, nr_rows, nr_cols) do
[
{row - 1, column - 1},
{row - 1, column},
{row - 1, column + 1},
{row, column - 1},
{row, column + 1},
{row + 1, column - 1},
{row + 1, column},
{row + 1, column + 1}
]
|> Enum.filter(fn {r, c} -> r >= 0 && r < nr_rows && c >= 0 && c < nr_cols end)
end

def sum_for_coordinate(row, column, nr_rows, nr_cols, source) do
if get_in(source, [row, column]) == "*" do
"*"
else
coordinate_list(row, column, nr_rows, nr_cols)
|> Enum.reduce(
0,
fn {r, c}, acc ->
if get_in(source, [r, c]) == " " do
acc
else
acc + 1
end
end
)
|> format_annotation()
end
end

def format_annotation(sum) do
if sum == 0 do
" "
else
Integer.to_string(sum)
end
end
end``````