Python – Reform K digit elements

Given the Python list, reform the element to have K digits in a single element.

Input : test_list = [223, 67, 332, 1, 239, 2, 931], K = 2 
Output : [22, 36, 73, 32, 12, 39, 29, 31] 
Explanation : Elements reformed to assign 2 digits to each element.

Input : test_list = [223, 67, 3327], K = 3 
Output : [223, 673, 327] 
Explanation : Elements reformed to assign 3 digits to each element. 

Method #1 : Using slicing + join() + loop

In this, we perform the task of joining all elements to a single string, then slice K digits, and reconvert to a list.

Python3

# Python3 code to demonstrate working of
# Reform K digit elements
# Using slicing + join() + loop

# initializing list
test_list = [223, 67, 332, 1, 239, 2, 931]

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

# initializing K
K = 2

# converting to string
temp = ''.join([str(ele) for ele in test_list])

# getting K digit slices
res = []
for idx in range(0, len(temp), K):
    res.append(int(temp[idx: idx + K]))

# printing result
print("Reforming K digits : " + str(res))

Output

The original list is : [223, 67, 332, 1, 239, 2, 931]
Reforming K digits : [22, 36, 73, 32, 12, 39, 29, 31]

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

Method #2 : Using list comprehension + join()

In this, the task of reforming the list is done using list comprehension. 

Python3

# Python3 code to demonstrate working of
# Reform K digit elements
# Using list comprehension + join()

# initializing list
test_list = [223, 67, 332, 1, 239, 2, 931]

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

# initializing K
K = 2

# converting to string
temp = ''.join([str(ele) for ele in test_list])

# getting K digit slices
# using 1 liner list comprehension
res = [int(temp[idx: idx + K]) for idx in range(0, len(temp), K)]

# printing result
print("Reforming K digits : " + str(res))

Output

The original list is : [223, 67, 332, 1, 239, 2, 931]
Reforming K digits : [22, 36, 73, 32, 12, 39, 29, 31]

Time Complexity: O(N), where n is the number of elements in the list “test_list”.
Auxiliary Space: O(N), where n is the number of elements in the list “test_list”.

Method #4: Using itertools and string concatenation

1. Import the ‘itertools’ module.
2. Convert each element of the original list to a string and concatenate it to a variable ‘temp’.
3. Using the ‘grouper’ function from itertools, group ‘temp’ into groups of K.
4. For each group, join the characters using the ‘join’ function and append the integer value of the resulting string to ‘res’.
5. Print the final ‘res’ list.

Python3

# Python3 code to demonstrate working of
# Reform K digit elements
# Using itertools and string concatenation
import itertools

# initializing list
test_list = [223, 67, 332, 1, 239, 2, 931]

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

# Initializing K
K = 2

# Converting to string
temp = "".join(str(ele) for ele in test_list)

# Getting K digit slices
res = [int("".join(group)) for group in itertools.zip_longest(*[iter(temp)]*K, fillvalue="")]

# Printing the result
print("Reforming K digits : " + str(res))

Output

The original list is : [223, 67, 332, 1, 239, 2, 931]
Reforming K digits : [22, 36, 73, 32, 12, 39, 29, 31]

Time complexity: O(N), where n is the length of the original list.
Auxiliary space: O(N), where n is the length of the original list (for storing the ‘temp’ string).