mirror of
https://github.com/wren-lang/wren.git
synced 2026-01-11 06:08:41 +01:00
60 lines
1.1 KiB
Ruby
60 lines
1.1 KiB
Ruby
|
def fannkuch(n)
|
||
|
|
p = (0..n).to_a
|
||
|
|
s = p.dup
|
||
|
|
q = p.dup
|
||
|
|
sign = 1
|
||
|
|
sum = maxflips = 0
|
||
|
|
while(true)
|
||
|
|
# flip.
|
||
|
|
|
||
|
|
if (q1 = p[1]) != 1
|
||
|
|
q[0..-1] = p
|
||
|
|
flips = 1
|
||
|
|
until (qq = q[q1]) == 1
|
||
|
|
q[q1] = q1
|
||
|
|
if q1 >= 4
|
||
|
|
i, j = 2, q1 - 1
|
||
|
|
while i < j
|
||
|
|
q[i], q[j] = q[j], q[i]
|
||
|
|
i += 1
|
||
|
|
j -= 1
|
||
|
|
end
|
||
|
|
end
|
||
|
|
q1 = qq
|
||
|
|
flips += 1
|
||
|
|
end
|
||
|
|
sum += sign * flips
|
||
|
|
maxflips = flips if flips > maxflips # New maximum?
|
||
|
|
|
||
|
|
end
|
||
|
|
# Permute.
|
||
|
|
|
||
|
|
if sign == 1
|
||
|
|
# Rotate 1<-2.
|
||
|
|
|
||
|
|
p[1], p[2] = p[2], p[1]
|
||
|
|
sign = -1
|
||
|
|
else
|
||
|
|
# Rotate 1<-2 and 1<-2<-3.
|
||
|
|
|
||
|
|
p[2], p[3] = p[3], p[2]
|
||
|
|
sign = 1
|
||
|
|
i = 3
|
||
|
|
while i <= n && s[i] == 1
|
||
|
|
return [sum, maxflips] if i == n # Out of permutations.
|
||
|
|
|
||
|
|
s[i] = i
|
||
|
|
# Rotate 1<-...<-i+1.
|
||
|
|
|
||
|
|
t = p.delete_at(1)
|
||
|
|
i += 1
|
||
|
|
p.insert(i, t)
|
||
|
|
end
|
||
|
|
s[i] -= 1 if i <= n
|
||
|
|
end
|
||
|
|
end
|
||
|
|
end
|
||
|
|
|
||
|
|
n = 9
|
||
|
|
sum, flips = fannkuch(n)
|
||
|
|
printf "%d\nPfannkuchen(%d) = %d\n", sum, n, flips
|