Python – Retain first N Elements of a String and Replace the Remaining by K

Given a String, retain first N elements and replace rest by K.

Input : test_str = ‘geeksforgeeks’, N = 5, K = “@” 
Output : geeks@@@@@@@@ 
Explanation : First N elements retained and rest replaced by K.

Input : test_str = ‘geeksforgeeks’, N = 5, K = “*” 
Output : geeks******** 
Explanation : First N elements retained and rest replaced by K.

Method #1 : Using * operator + len() + slicing

In this, slicing is used to retain N, and then the length of remaining is extracted by subtracting the total length extracted by len(), from N, and then repeat K char using * operator.

Python3

# Python3 code to demonstrate working of
# Retain N and Replace remaining by K
# Using * operator + len() + slicing

# initializing string
test_str = 'geeksforgeeks'

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

# initializing length needed
N = 4

# initializing remains char
K = "@"

# using len() and * operator to solve problem
res = test_str[:N] + K * (len(test_str) - N)

# printing result
print("The resultant string : " + str(res))

Output

The original string is : geeksforgeeks
The resultant string : geek@@@@@@@@@

Time Complexity: O(n) -> string slicing

Auxiliary Space: O(n)

Method #2 : Using ljust() + slicing + len()

In this, the task of assigning remaining characters is done using ljust, rather than the * operator.

Python3

# Python3 code to demonstrate working of
# Retain N and Replace remaining by K
# Using ljust() + slicing + len()

# initializing string
test_str = 'geeksforgeeks'

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

# initializing length needed
N = 4

# initializing remains char
K = "@"

# ljust assigns K to remaining string
res = test_str[:N].ljust(len(test_str), K)

# printing result
print("The resultant string : " + str(res))

Output

The original string is : geeksforgeeks
The resultant string : geek@@@@@@@@@

Time Complexity: O(n) -> string slicing

Auxiliary Space: O(n)

Method 3 (Using replace() method):

Use the replace method to replace the characters except the first N elements.

Python3

# Python3 code to demonstrate working of
# Retain N and Replace remaining by K


def changedString(test_str):

    res = test_str.replace(test_str[N:], K*len(test_str[N:]))

    # Printing result
    return str(res)


# Driver code
if __name__ == '__main__':

    # Initializing string
    test_str = 'geeksforgeeks'

    # Initializing length needed
    N = 4

    # Initializing remains char
    K = "@"

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

    print("The resultant string is : ", end = "")
    print(changedString(test_str))

Output

The original string is : geeksforgeeks
The resultant string is : geek@@@@@@@@@

Time Complexity: O(n) -> average of string slicing and replace function

Auxiliary Space: O(n)