Python – Kth word replace in String

Sometimes, while working with String list, we can have a problem in which we need to replace the most Kth word of string. This problem has many applications in the web development domain. Let’s discuss a way in which this problem can be solved. 

Method 1: Using split() + join() This is way in which we can perform this task. In this, we break elements into parts and then return the Kth value and perform the addition of new element using join(). 

Python3

# Python3 code to demonstrate working of
# Kth word replace in String
# using split() + join()

# initializing string
test_str = "GFG is good"

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

# initializing replace string
rep_str = "best"

# initializing K
K = 1

# Kth word replace in String
# using split() + join()
temp = test_str.split(' ')
res = " ".join(temp[: K]  + [rep_str] + temp[K + 1 :])

# printing result
print("The String after performing replace : " + res)

Output : 

The original string is : GFG is good
The String after performing replace : GFG best good

Time Complexity: O(n), where n is the length of the given string.
Auxiliary Space: O(n + m), where n and m are the length of original string and replace string respectively.

Method 2: Using split() and join() methods without slicing

Python3

# Python3 code to demonstrate working of
# Kth word replace in String
# using split() + join()

# initializing string
test_str = "GFG is good"

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

# initializing replace string
rep_str = "best"

# initializing K
K = 1

# Kth word replace in String
# using split() + join()
temp = test_str.split(' ')
temp[K]=rep_str
res=" ".join(temp)

# printing result
print("The String after performing replace : " + res)

Output

The original string is : GFG is good
The String after performing replace : GFG best good

Time Complexity: O(n), where n is the length of the given string.
Auxiliary Space: O(n + m), where n and m are the length of original string and replace string respectively.

Method #3: Using re.sub() and re.findall()

Python3

import re

# initializing string
test_str = "GFG is good"

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

# initializing replace string
rep_str = "best"

# initializing K
K = 1

# Kth word replace in String
# using re.sub() and re.findall()
temp = re.findall(r'\b\w+\b', test_str)
temp[K] = rep_str
res = re.sub(r'\b\w+\b', lambda x: temp.pop(0), test_str)

# printing result
print("The String after performing replace : " + res)
#This code is contributed by Edula Vinay Kumar Reddy

Output

The original string is : GFG is good
The String after performing replace : GFG best good

This method uses regular expression to find all words in the string and replace the Kth word with the new one using re.sub() function.

Time Complexity: O(n), where n is the length of the given string.
Auxiliary Space: O(n + m), where n and m are the length of original string and replace string respectively.