Python – Get all numbers combinations in list

Sometimes, while working with Python lists, we can have a problem in which we need to concatenate each number with other create new number. This kind of problem is peculiar but can have application in many domains such as day-day programming and gaming. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [7, 3, 4, 5] Output : [73, 74, 75, 34, 35, 45] Input : test_list = [2, 5] Output : [25]

Method #1 : Using list comprehension + combination() The combination of above functions can be used to solve this problem. In this, we perform the task of finding all combination using combination() and f-strings can be used to perform concatenation. 

Python3

# Python3 code to demonstrate working of
# All numbers combinations
# Using list comprehension + combinations
from itertools import combinations

# initializing list
test_list = [59, 236, 31, 38, 23]

# printing original list
print("The original list : " + str(test_list))

# All numbers combinations
# Using list comprehension + combinations
res = [int(f"{x}{y}") for x, y in combinations(test_list, 2)]

# printing result
print("All numbers combinations : " + str(res))

Output : 

The original list : [59, 236, 31, 38, 23] All numbers combinations : [59236, 5931, 5938, 5923, 23631, 23638, 23623, 3138, 3123, 3823]

Time Complexity: O(n) where n is the number of elements in the list “test_list”.  list comprehension + combination() performs n number of operations.
Auxiliary Space: O(n), extra space is required where n is the number of elements in the list

Method #2 : Using loop + str() + int() The combination of above functions can be used to solve this problem. In this we perform the task of forming combinations using brute force and type conversions in nested loop. This also outputs reverse combinations. 

Python3

# Python3 code to demonstrate working of
# All numbers combinations
# Using loop + str() + int()
from itertools import combinations

# initializing list
test_list = [59, 236, 31, 38, 23]

# printing original list
print("The original list : " + str(test_list))

# All numbers combinations
# Using loop + str() + int()
res = []
for i in test_list:
    for j in test_list:
        if j != i:
           res.append(int(str(i) + str(j)))

# printing result
print("All numbers combinations : " + str(res))

Output : 

The original list : [59, 236, 31, 38, 23] All numbers combinations : [59236, 5931, 5938, 5923, 23659, 23631, 23638, 23623, 3159, 31236, 3138, 3123, 3859, 38236, 3831, 3823, 2359, 23236, 2331, 2338]