Created
June 20, 2017 14:40
-
-
Save ph87/56137f52f32fc29910fbccb92731ef2d to your computer and use it in GitHub Desktop.
from python itertools
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
def permutations(iterable, r=None): | |
# permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC | |
# permutations(range(3)) --> 012 021 102 120 201 210 | |
pool = tuple(iterable) | |
n = len(pool) | |
r = n if r is None else r | |
if r > n: | |
return | |
indices = range(n) | |
cycles = range(n, n-r, -1) | |
yield tuple(pool[i] for i in indices[:r]) | |
while n: | |
for i in reversed(range(r)): | |
cycles[i] -= 1 | |
if cycles[i] == 0: | |
indices[i:] = indices[i+1:] + indices[i:i+1] | |
cycles[i] = n - i | |
else: | |
j = cycles[i] | |
indices[i], indices[-j] = indices[-j], indices[i] | |
yield tuple(pool[i] for i in indices[:r]) | |
break | |
else: | |
return |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment