CODEWITHSUNDEEP
pythonpython-3.xlistcombinations
Saradoc
Saradoc

Reputation: 103

Find all ways to decide list into three

Like the title says, how can I find all of the ways a list can be divided into three lists? For example 1,2,3 would return 

[1, 2, 3]
[1] [2] [3]
[1, 2] [3] [ ]
[1] [2, 3] [ ]
[1, 3] [2] [ ]

I've tried a bunch of stuff but just can't seem to get it. Thanks!

Upvotes: 1

Views: 83

Answers (2)

Ougaga
Ougaga

Reputation: 127

you could use combinations from the lib itertools

import itertools

my_list = [1, 2, 3]

for i in range(len(my_list)):
    print(list(itertools.combinations(my_list, i + 1)))

which outputs

[(1,), (2,), (3,)]
[(1, 2), (1, 3), (2, 3)]
[(1, 2, 3)]

now you can add the length of each list and add the missing empty lists (to complete having 3 lists) and voila - you have your result

Upvotes: 2

HVD
HVD

Reputation: 56

Here is a possible solution:

import itertools

# your input data list
a = [1, 2, 3]

# util function to convert list of tuples to list of list
f = lambda x: [list(i) if isinstance(i, tuple) else i for i in x]

# list1 is all combinations of sublists having length = 1,2,..length_of_a from input list `a` and empty list [] 
list1 = []
for i in range(1, len(a)+1):
    list1.extend(itertools.combinations(a, i))
list1.extend([()]*(len(a)-1))

# list2 is all combinations of sublists having length = length_of_a from the list1
list2 = list(set(itertools.combinations(list1, len(a))))

#  filtering out and converting list of tuples for the final results
results = [f(i) for i in list2 if sum(itertools.chain(*i)) == sum(a) and set(itertools.chain(*i)) == set(a)]
results.append(a)

# print out the results
for r in results:
    print(r)

Outputs:

[[1, 2, 3], [], []]

[[3], [1, 2], []]

[[1], [2], [3]]

[[2], [1, 3], []]

[[1], [2, 3], []]

[1, 2, 3]

Upvotes: 0

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