Created
September 22, 2011 15:57
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Permutations in Python (from Python website)
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// directly from http://docs.python.org/library/itertools.html | |
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 |
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