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72 lines
2.3 KiB
72 lines
2.3 KiB
4 years ago
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bignum = require "_openssl.bignum"
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function find(card, deck, times)
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local revert = false
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local increment = bignum.new(0)
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local multiply = bignum.new(1)
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for line in io.lines(arg[1]) do
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if line:find("^deal into new stack$") then
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revert = not revert
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elseif line:find("^cut %-?%d+$") then
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local val = tonumber(line:match("^cut (%-?%d+)$"))
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if not revert then
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increment = (increment - val) % deck
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else
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increment = (increment + val) % deck
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end
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elseif line:find("^deal with increment %d+$") then
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local val = tonumber(line:match("^deal with increment (%d+)$"))
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multiply = (multiply * val) % deck
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increment = (increment * val) % deck
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if revert then
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increment = (increment + (val - 1)) % deck
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end
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end
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end
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print(card, multiply, increment, deck)
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card = (card * multiply * times + increment * times) % deck
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if revert then
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card = deck - (card + 1)
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end
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return card
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end
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function revfind(card, deck, times)
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local revert = false
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local increment = bignum.new(0)
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local multiply = bignum.new(1)
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for line in io.lines(arg[1]) do
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if line:find("^deal into new stack$") then
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revert = not revert
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elseif line:find("^cut %-?%d+$") then
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local val = tonumber(line:match("^cut (%-?%d+)$"))
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if not revert then
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increment = (increment - val) % deck
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else
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increment = (increment + val) % deck
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end
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elseif line:find("^deal with increment %d+$") then
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local val = tonumber(line:match("^deal with increment (%d+)$"))
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multiply = (multiply * val) % deck
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increment = (increment * val) % deck
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if revert then
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increment = (increment + (val - 1)) % deck
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end
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end
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end
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print(card, multiply, increment, deck)
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card = (card * multiply * times + increment * times) % deck
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if revert then
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card = deck - (card + 1)
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end
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return card
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end
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print("Part 1:", find(2019, 10007, 1))
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print("Part 2:", find(2020, 119315717514047, 101741582076661))
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print("Part 1:", revfind(7744, 10007, 1))
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print("Part 2:", revfind(2020, 119315717514047, 101741582076661))
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