CODEWITHSUNDEEP
python
Paul R
Paul R

Reputation: 2797

How to calculate permutations with repetitions in python

How to find number of permutations when items are repeated? For example, for the string aab I want the following output: aab, aba, baa.

Upvotes: 1

Views: 2077

Answers (3)

MarredCheese
MarredCheese

Reputation: 20801

more-itertools.distinct_permutations(iterable)

Yields successive distinct permutations of the elements in iterable.

Equivalent to set(permutations(iterable)), except duplicates are not generated and thrown away. For larger input sequences, this is much more efficient.

from more_itertools import distinct_permutations

for p in distinct_permutations('aab'):
    print(''.join(p))

# baa
# aba
# aab

Installation:

pip install more-itertools

Upvotes: 2

Acsor
Acsor

Reputation: 1061

You can use the standard-library itertools module:

from itertools import permutations


iterable = "aab"
print(set(permutations(iterable, len(iterable))))

By executing that code, I get the following output:

None@vacuum:~$ python3.6 ./test.py 
{('b', 'a', 'a'), ('a', 'b', 'a'), ('a', 'a', 'b')}

Upvotes: 2

Horia Coman
Horia Coman

Reputation: 8781

The following should work:

import itertools
set(itertools.permutations('aab'))

The permutations will produce all permutations, but it will repeat some of it's output because it can't differentiate between a1 a2 b and a2 a1 b. Here a1 is the first occurrence of a, and a2 the second. So you need to just keep the unique elements, and a set is a good way to do that, as the constructor transforms the input iterable into a unique collection.

Upvotes: 0

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