Python Program to split string into k sized overlapping strings

Given a string, the task is to write a Python program to extract overlapping consecutive string slices from the original string according to size K. 

Example:

Input : test_str = ‘Geeksforgeeks’, K = 4

Output : [‘Geek’, ‘eeks’, ‘eksf’, ‘ksfo’, ‘sfor’, ‘forg’, ‘orge’, ‘rgee’, ‘geek’, ‘eeks’]

Explanation : Consecutive overlapping 4 sized strings are output.

Input : test_str = ‘Geeksforgeeks’, K = 6

Output : [‘Geeksf’, ‘eeksfo’, ‘eksfor’, ‘ksforg’, ‘sforge’, ‘forgee’, ‘orgeek’, ‘rgeeks’]

Explanation : Consecutive overlapping 6 sized strings are output.

Method 1: Using islice() + generator function + join()

In this, windows of size K are extracted using the islice(), and results are yielded in an intermediate way using yield. The final results are joined using join(). 

Python3

# Python3 code to demonstrate working of
# Overlapping consecutive K splits
# Using islice() + generator function + join()
from itertools import islice

# generator function
def over_slice(test_str, K):
    itr = iter(test_str)
    res = tuple(islice(itr, K))
    if len(res) == K:
        yield res
    for ele in itr:
        res = res[1:] + (ele,)
        yield res

# initializing string
test_str = 'Geeksforgeeks'

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

# initializing K
K = 4

# calling generator function
res = ["".join(ele) for ele in over_slice(test_str, K)]

# printing result
print("Overlapping windows : " + str(res))

Output:

The original string is : Geeksforgeeks

Overlapping windows : [‘Geek’, ‘eeks’, ‘eksf’, ‘ksfo’, ‘sfor’, ‘forg’, ‘orge’, ‘rgee’, ‘geek’, ‘eeks’]

Method 2: Using list comprehension + slicing

In this example, intermediate slices are performed using a slicing operation in a more pythonic way. Each window is extracted using slice notation.

Python3

# Python3 code to demonstrate working of
# Overlapping consecutive K splits
# Using list comprehension + slicing

# initializing string
test_str = 'Geeksforgeeks'

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

# initializing K
K = 4

# extracting window using slicing
res = [test_str[idx:idx + K] for idx in range(len(test_str) - K + 1)]

# printing result
print("Overlapping windows : " + str(res))

Output:

The original string is : Geeksforgeeks

Overlapping windows : [‘Geek’, ‘eeks’, ‘eksf’, ‘ksfo’, ‘sfor’, ‘forg’, ‘orge’, ‘rgee’, ‘geek’, ‘eeks’] 

The Time and Space Complexity of all the methods is :

Time Complexity: O(n)

Space Complexity: O(n)

Method 3:  Using recursion :

Python3

# Python3 code to demonstrate working of
# Overlapping consecutive K splits
# Using recursion

# initializing string
test_str = 'Geeksforgeeks'

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

# initializing K
K = 4

# recursive function
def over_slice(test_str, K, res = []):
    # if length of string is less
    if (len(test_str) < K):
        return

    # append the string
    res.append(test_str[:K])

    # call recursively
    over_slice(test_str[1:], K, res)

    # return result
    return res

# calling recursive function
res = over_slice(test_str, K)

# printing result
print("Overlapping windows : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

Output

The original string is : Geeksforgeeks
Overlapping windows : ['Geek', 'eeks', 'eksf', 'ksfo', 'sfor', 'forg', 'orge', 'rgee', 'geek', 'eeks']

Time Complexity: O(n)

Auxiliary Space: O(n)

Method 4 : using the windowed() function from the more_itertools module. 

This function takes an iterable and a window size, and returns an iterator over overlapping windows of the specified size. 

The steps for this approach are:

Import the windowed() function from the more_itertools module.
Initialize a list containing the string to be split.
Use the windowed() function to get an iterator over overlapping windows of size K.
Use a list comprehension to join each window of characters into a string.
Return the list of overlapping windows.

Python3

# Python3 code to demonstrate working of
# Overlapping consecutive K splits
# Using windowed() function from more_itertools module

from more_itertools import windowed

# initializing string
test_str = 'Geeksforgeeks'

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

# initializing K
K = 4

# converting string to list of characters
str_list = list(test_str)

# using windowed() function to get overlapping windows
windows = windowed(str_list, K, step=1)

# using list comprehension to join windows into strings
res = ["".join(w) for w in windows]

# printing result
print("Overlapping windows : " + str(res))

OUTPUT : 
The original string is : Geeksforgeeks
Overlapping windows : ['Geek', 'eeks', 'eksf', 'ksfo', 'sfor', 'forg', 'orge', 'rgee', 'geek', 'eeks']

The time complexity of this approach is O(N), since the windowed() function is a generator and only generates the windows as they are needed, without precomputing them all at once. 

The auxiliary space complexity is O(NK), since we need to store all the overlapping windows in a list.