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s = "abcdefgh"
def rl(s, c)
s = s.dup
a = s.index c
s = s.slice!(-1) + s
a.times {
s = s.slice!(-1) + s
}
s = s.slice!(-1) + s if a >= 4
s
end
File.readlines("day21").each { |line|
case line
when /reverse positions (\d+) through (\d+)/
a, b = $1.to_i, $2.to_i
s[a..b] = s[a..b].reverse
when /rotate based on position of letter (.)/
s = rl(s, $1)
when /rotate right (\d+) step/
$1.to_i.times {
s = s.slice!(-1) + s
}
when /rotate left (\d+) step/
$1.to_i.times {
s = s + s.slice!(0)
}
when /swap position (\d+) with position (\d+)/
a, b = $1.to_i, $2.to_i
s[a], s[b] = s[b], s[a]
when /move position (\d+) to position (\d+)/
s.insert($2.to_i, s.slice!($1.to_i))
when /swap letter (.) with letter (.)/
s.tr! $1+$2, $2+$1
else
abort "what is #{line.dump}"
end
}
p s # gfdhebac
def brute(s, a)
s = s.dup
(1..s.size).each { |i|
t = s.dup
i.times {
t = t.slice!(-1) + t
}
if rl(t, a) == s
return t
end
}
abort "oops"
end
s = "fbgdceah"
File.readlines("day21").reverse_each { |line|
case line
when /reverse positions (\d+) through (\d+)/ #idem
a, b = $1.to_i, $2.to_i
s[a..b] = s[a..b].reverse
when /rotate based on position of letter (.)/ #brute
s = brute(s, $1)
when /rotate left (\d+) step/ #swap
$1.to_i.times {
s = s.slice!(-1) + s
}
when /rotate right (\d+) step/ #swap
$1.to_i.times {
s = s + s.slice!(0)
}
when /swap position (\d+) with position (\d+)/ #idem
a, b = $1.to_i, $2.to_i
s[a], s[b] = s[b], s[a]
when /move position (\d+) to position (\d+)/ #swap
s.insert($1.to_i, s.slice!($2.to_i))
when /swap letter (.) with letter (.)/ #idem
s.tr! $1+$2, $2+$1
else
abort "what is #{line.dump}"
end
}
p s
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