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#!/opt/local/bin/lua
--
-- See ../README.md
--
--
-- Run as: lua ch-1.lua < input-file
--
--
-- We're reading years from standard input, one year per line, outputting
-- years from the sexagenary cycle [1]. This is slightly more than what
-- the challenge ask; the challenge asks to output the heavenly stem [2],
-- and the earthly branch [3]. But we also output its Yin/Yang.
--
-- [1] https://en.wikipedia.org/wiki/Sexagenary_cycle
-- [2] https://en.wikipedia.org/wiki/Heavenly_Stems
-- [3] https://en.wikipedia.org/wiki/Earthly_Branches
--
--
-- Each of the cycles have been rotated so the first entry corresponds to
-- the year 0 in the Proleptic Gregorian calendar. (We're using the
-- convention of having a year 0, as per ISO 8601).
-- That way, we can just mod the year with the number of entries, without
-- first having to subtract something from the year.
--
-- The heavenly stems last for 2 years, so we just duplicate the entries.
--
local yin_yang = {"Yang", "Yin"};
local heavenly_stems = {"Metal", "Metal", "Water", "Water",
"Wood", "Wood", "Fire", "Fire",
"Earth", "Earth"};
local earthly_branches = {"Monkey", "Rooster", "Dog", "Pig",
"Rat", "Ox", "Tiger", "Rabbit",
"Dragon", "Snake", "Horse", "Goat"};
for line in io . lines () do
local year = tonumber (line)
io . write (yin_yang [1 + (year % #yin_yang)], " ",
heavenly_stems [1 + (year % #heavenly_stems)], " ",
earthly_branches [1 + (year % #earthly_branches)], "\n")
end
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