55 lines
1.8 KiB
Elixir
55 lines
1.8 KiB
Elixir
defmodule Day18Part2 do
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def run do
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File.stream!("input")
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|> Stream.map(&tokenize/1)
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|> Stream.map(&to_ast/1)
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|> Stream.map(&evaluate/1)
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|> Enum.sum()
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|> IO.puts()
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end
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def tokenize(line) do
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line
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|> String.graphemes()
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|> Stream.reject(fn char -> char in [" ", "\n"] end)
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|> Enum.map(fn
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symbol when symbol in ["*", "+", "(", ")"] -> symbol
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num -> {:num, String.to_integer(num)}
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end)
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end
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def to_ast(line), do: to_ast(line, nil, nil, [])
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def to_ast([], ast, nil, []), do: ast
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def to_ast([], ast, nil, later), do: ast_later(Enum.reverse([ast | later]), nil, nil)
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def to_ast(["+" | rest], left, nil, later), do: to_ast(rest, left, "+", later)
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def to_ast(["*" | rest], left, nil, later), do: to_ast(rest, nil, nil, ["*", left | later])
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def to_ast(["(" | rest], nil, op, later) do
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{new_left, rest} = to_ast(rest)
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to_ast(rest, new_left, op, later)
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end
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def to_ast(["(" | rest], left, op, later) do
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{new_left, rest} = to_ast(rest)
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to_ast([left | rest], new_left, op, later)
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end
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def to_ast([")" | rest], ast, nil, later) do
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ast = ast_later(Enum.reverse([ast | later]), nil, nil)
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{ast, rest}
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end
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def to_ast([ast | rest], nil, nil, later), do: to_ast(rest, ast, nil, later)
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def to_ast([right | rest], left, "+", later), do: to_ast(rest, {"+", left, right}, nil, later)
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def ast_later([], ast, nil), do: ast
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def ast_later(["*" | rest], left, nil), do: ast_later(rest, left, "*")
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def ast_later([left | rest], nil, nil), do: ast_later(rest, left, nil)
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def ast_later([right | rest], left, "*"), do: ast_later(rest, {"*", left, right}, nil)
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def evaluate({:num, num}), do: num
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def evaluate({"+", left, right}), do: evaluate(left) + evaluate(right)
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def evaluate({"*", left, right}), do: evaluate(left) * evaluate(right)
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end
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Day18Part2.run()
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