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Contents
defmodule Connect do
@doc """
Calculates the winner (if any) of a board
using "O" as the white player
and "X" as the black player
"""
@spec result_for([String.t()]) :: :none | :black | :white
def result_for(board) do
cond do
black_wins?(board) -> :black
white_wins?(board) -> :white
true -> :none
end
end
defp black_wins?(board) do
board
|> Enum.with_index()
|> Enum.any?(fn {row, index} ->
String.first(row) == "X" && black_wins?(board, [{index, 0}])
end)
end
defp black_wins?(board, [{_, y} | _]) when y + 1 == byte_size(hd(board)), do: true
defp black_wins?(board, history = [last_loc | _]) do
last_loc
|> locs_next_to(history)
|> Enum.filter(&(get_loc(board, &1) == "X"))
|> Enum.any?(&black_wins?(board, [&1 | history]))
end
defp white_wins?(board) do
board
|> hd
|> String.graphemes()
|> Enum.with_index()
|> Enum.any?(fn {spot, index} ->
spot == "O" && white_wins?(board, [{0, index}])
end)
end
defp white_wins?(board, [{x, _} | _]) when x + 1 == length(board), do: true
defp white_wins?(board, history = [last_loc | _]) do
last_loc
|> locs_next_to(history)
|> Enum.filter(&(get_loc(board, &1) == "O"))
|> Enum.any?(&white_wins?(board, [&1 | history]))
end
defp locs_next_to({x, y}, history) do
[
{x, y - 1},
{x, y + 1},
{x + 1, y},
{x - 1, y},
{x + 1, y - 1},
{x - 1, y + 1}
]
|> Enum.filter(&valid_next_loc(&1, history))
end
defp valid_next_loc({x, y}, history) do
x >= 0 && y >= 0 && !({x, y} in history)
end
defp get_loc(board, {x, y}) do
row = Enum.at(board, x)
row && String.at(row, y)
end
end
Version data entries
69 entries across 69 versions & 1 rubygems