Python – K length Combinations from given characters

Given a string, generate K-length combinations in a one-liner.

Input : test_str = ‘gfg’, K = 3 
Output : [‘ggg’, ‘ggf’, ‘ggg’, ‘gfg’, ‘gff’, ‘gfg’, ‘ggg’, ‘ggf’, ‘ggg’, ‘fgg’, ‘fgf’, ‘fgg’, ‘ffg’, ‘fff’, ‘ffg’, ‘fgg’, ‘fgf’, ‘fgg’, ‘ggg’, ‘ggf’, ‘ggg’, ‘gfg’, ‘gff’, ‘gfg’, ‘ggg’, ‘ggf’, ‘ggg’] 
Explanation : All combinations of K length extracted.

Input : test_str = ‘G4G’, K = 2 
Output : [‘GG’, ‘G4’, ‘GG’, ‘4G’, ’44’, ‘4G’, ‘GG’, ‘G4’, ‘GG’] 
Explanation : All combinations of K length extracted. 

Method #1 : Using itertools.product() + join() + map()

The task can be performed by product() using repeat param, but returns the result in a tuples list of individual characters. These all can be joined using join() and map().

Python3

# Python3 code to demonstrate working of
# K length Combinations from given characters shorthand
# Using itertools.product() + join() + map()
from itertools import product

# initializing string
test_str = 'gf4g'

# printing original string
print("The original string is : " + str(test_str))

# initializing K
K = 2

# map and join() used to change return data type
res = list(map(''.join, product(test_str, repeat = K)))

# printing result
print("The generated Combinations : " + str(res))

Output

The original string is : gf4g
The generated Combinations : ['gg', 'gf', 'g4', 'gg', 'fg', 'ff', 'f4', 'fg', '4g', '4f', '44', '4g', 'gg', 'gf', 'g4', 'gg']

Time Complexity: O(n)
Auxiliary Space: O(1)

Method #2 : Using itertools.product() + list comprehension

In this, list comprehension is used for the task of joining elements.

Python3

# Python3 code to demonstrate working of
# K length Combinations from given characters shorthand
# Using itertools.product() + join() + map()
from itertools import product

# initializing string
test_str = 'gfg'

# printing original string
print("The original string is : " + str(test_str))

# initializing K
K = 2

# list comprehension + join() used to change return data type
res = [''.join(ele) for ele in product(test_str, repeat = K)]

# printing result
print("The generated Combinations : " + str(res))

Output

The original string is : gfg
The generated Combinations : ['gg', 'gf', 'gg', 'fg', 'ff', 'fg', 'gg', 'gf', 'gg']

Time Complexity: O(n)
Auxiliary Space: O(1)