find binary permutations in python

Question

I'm looking for a way to find all binary permutations with x amount of '1'. For example:

(length = 2) x = 1 (so: find all permutations of 1 and 0 with the length 2 which have one 1 in them)

l = ['01', '10']

x = 2 (so: find all permutations of 1 and 0 with the length 2 which have two 1 in them)

l = ['11']

so far i have this which calculates all possible permutations but i'm not sure how to 'filter' them by the '1's (especially when the size is 7 for example)

pre = list(map(''.join, itertools.product('01',repeat=2)))

i'm looking for something faster/better than my for loop which counts '1'.

Andrzej Pronobis · Accepted Answer · 2015-05-28 20:15:55Z

2

Try this:

l=7
x=6
set(itertools.permutations([1]*x + [0]*(l-x)))

results in:

{(0, 1, 1, 1, 1, 1, 1),
 (1, 0, 1, 1, 1, 1, 1),
 (1, 1, 0, 1, 1, 1, 1),
 (1, 1, 1, 0, 1, 1, 1),
 (1, 1, 1, 1, 0, 1, 1),
 (1, 1, 1, 1, 1, 0, 1),
 (1, 1, 1, 1, 1, 1, 0)}

answered May 28, 2015 at 20:15

Andrzej Pronobis

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