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Contents
defmodule Dominoes do
@type domino :: {1..6, 1..6}
@doc """
chain?/1 takes a list of domino stones and returns boolean indicating if it's
possible to make a full chain
"""
@spec chain?(dominoes :: [domino] | []) :: boolean
def chain?([]), do: true
def chain?([{a, a}]), do: true
def chain?([{_a, _b}]), do: false
def chain?(dominoes), do: [] !== chains(dominoes)
def chains([first | rest]) do
for combi <- permutations(rest), {:ok, result} <- chain(combi, [], first), do: result
end
defp chain([], [{a, _} | _] = acc, {_, a} = last), do: [{:ok, acc ++ [last]}]
defp chain([], _acc, _last), do: [{:error, :ends_not_same}]
defp chain([{b, c} = this | rest], acc, {_, b} = next) when b != c do
chain(rest, acc ++ [next], this)
end
defp chain([{c, b} | rest], acc, {_, b} = next) when b != c do
chain(rest, acc ++ [next], {b, c})
end
defp chain([{b, b} = this | rest], acc, {_, b} = next) do
chain(rest, acc ++ [next], this)
end
defp chain(_a, _b, _c), do: [{:error, :no_followup}]
defp permutations([]), do: [[]]
defp permutations(list) do
for h <- list, t <- permutations(list -- [h]), do: [h | t]
end
end
Version data entries
119 entries across 119 versions & 1 rubygems