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danielpilon's solution

to Minesweeper in the Elixir Track

Published at Jun 30 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: []

  def annotate(board),
    do:
      board
      |> map_coordinates()
      |> annotate_coordinates()
      |> to_board()

  defp map_coordinates(board),
    do:
      board
      |> Stream.with_index()
      |> Stream.flat_map(&coordinates/1)
      |> Enum.into(%{})

  defp coordinates({row, row_index}) do
    row
    |> to_charlist()
    |> Stream.with_index()
    |> Stream.map(fn {char, column_index} -> {{row_index, column_index}, char} end)
  end

  defp annotate_coordinates(coordinates),
    do:
      coordinates
      |> Enum.reduce(coordinates, &adjacent_mines/2)

  defp adjacent_mines({_coordinate, ?*}, coordinates), do: coordinates

  defp adjacent_mines({{row, column} = coordinate, mines}, coordinates),
    do:
      mines
      |> step_increment(coordinates[{row - 1, column}])
      |> step_increment(coordinates[{row - 1, column + 1}])
      |> step_increment(coordinates[{row - 1, column - 1}])
      |> step_increment(coordinates[{row, column - 1}])
      |> step_increment(coordinates[{row, column + 1}])
      |> step_increment(coordinates[{row + 1, column - 1}])
      |> step_increment(coordinates[{row + 1, column}])
      |> step_increment(coordinates[{row + 1, column + 1}])
      |> update_mine_count(coordinates, coordinate)

  defp step_increment(?\s, ?*), do: ?1
  defp step_increment(mines, ?*), do: mines + 1
  defp step_increment(mines, _value), do: mines

  defp update_mine_count(mines, coordinates, coordinate),
    do: Map.put(coordinates, coordinate, mines)

  defp to_board(coordinates),
    do:
      coordinates
      |> Enum.group_by(fn {{row, _column}, _value} -> row end, fn {_coordinate, value} ->
        value
      end)
      |> Enum.map(fn {_index, row} -> row |> to_string end)
end

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