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advent-of-code/2017/day24/day24.erl

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3.6 KiB
Erlang
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2017-12-24 02:02:16 -05:00
-module(day24).
-export([start/0]).
read_input(Filename)
-> { ok, Input } = file:read_file(Filename),
lists:map(fun(X) ->
[A,B|_] = re:split(X, "/"),
{ AInt, _ } = string:to_integer(A),
{ BInt, _ } = string:to_integer(B),
{ AInt, BInt }
end, re:split(string:chomp(Input), "\n")).
strongest_bridge(Input)
-> strongest_bridge(Input, 0, 0, []).
strongest_bridge([], _LastEdge, Sum, Train)
-> { Sum, Train };
strongest_bridge(Input, LastEdge, Sum, Train)
-> { Matching, _ } = lists:partition(fun(X) ->
{ A, B } = X,
(A == LastEdge) or (B == LastEdge)
end, Input),
if length(Matching) == 0 -> { Sum, Train };
true ->
MatchingSums = lists:map(fun(X) ->
{ _, Remaining } = lists:partition(fun(Y) -> Y == X end, Input),
{ A, B } = X,
NewTrain = lists:append(Train, [X]),
NewSum = Sum + A + B,
if A == LastEdge -> strongest_bridge(Remaining, B, NewSum, NewTrain);
true -> strongest_bridge(Remaining, A, NewSum, NewTrain)
end
end, Matching),
[FirstSum|_] = lists:sort(fun(X, Y) ->
{ A, _ } = X,
{ B, _ } = Y,
B =< A
end, MatchingSums),
FirstSum
end.
longest_bridge(Input)
-> longest_bridge(Input, 0, 0, []).
longest_bridge([], _LastEdge, Sum, Train)
-> { Sum, Train };
longest_bridge(Input, LastEdge, Sum, Train)
-> { Matching, _ } = lists:partition(fun(X) ->
{ A, B } = X,
(A == LastEdge) or (B == LastEdge)
end, Input),
if length(Matching) == 0 -> { Sum, Train };
true ->
MatchingSums = lists:map(fun(X) ->
{ _, Remaining } = lists:partition(fun(Y) -> Y == X end, Input),
{ A, B } = X,
NewTrain = lists:append(Train, [X]),
NewSum = Sum + A + B,
if A == LastEdge -> longest_bridge(Remaining, B, NewSum, NewTrain);
true -> longest_bridge(Remaining, A, NewSum, NewTrain)
end
end, Matching),
[FirstSum|_] = lists:sort(fun(X, Y) ->
{ A, I } = X,
{ B, J } = Y,
if length(I) == length(J) -> B =< A;
true -> length(J) =< length(I)
end
end, MatchingSums),
FirstSum
end.
start()
-> SampleInput = read_input("sample"),
io:fwrite("~p~n", [strongest_bridge(SampleInput)]),
io:fwrite("~p~n", [longest_bridge(SampleInput)]),
ProblemInput = read_input("problem"),
io:fwrite("~p~n", [strongest_bridge(ProblemInput)]),
io:fwrite("~p~n", [longest_bridge(ProblemInput)]).