Python – Replace occurrences by K except first character

Given a String, the task is to write a Python program to replace occurrences by K of character at 1st index, except at 1st index.

Examples:

Input : test_str = 'neveropenforLazyroar', K = '@'
Output : Lazyroarfor@eeksfor@eeks

Explanation : All occurrences of g are converted to @ except 0th index.

Input : test_str = 'neveropen', K = '#'
Output : Lazyroarfor#eeks

Explanation : All occurrences of g are converted to # except 0th index.

Method #1 : Using slicing + replace()

In this, we perform task of replacing entire string from 2nd character with K of the character occurring at 1st index. The result is prefix joined by first character.

Output:

The original string is : neveropenforLazyroar
Replaced String : Lazyroarfor$eeksfor$eeks

Method #2 : Using replace()

In this, replace() is called twice for task of replacing all occurrences, and then just reverse replace the first occurrence.

Output:

The original string is : neveropenforLazyroar
Replaced String : Lazyroarfor$eeksfor$eeks

The time and space complexity for all the methods are the same:

Time Complexity: O(n)

Auxiliary Space: O(n)

Method #3: Using loops

The original string is : neveropenforLazyroar
Replaced String : Lazyroarfor$eeksfor$eeks

Time Complexity: O(n), where n is length of test_str string.

Auxiliary Space: O(n), where n is length of string x to store the result.

Method #4: Using list comprehension

The given program replaces all occurrences of the first character in the given string with a new character K except for the first occurrence. Here is the step-by-step approach to implement this program in Python:

• Initialize the input string – test_str.
• Print the original string.
• Initialize a new character K with any desired character value.
• Using list comprehension, iterate through each character of the input string except for the first character. If the character is equal to the first character and it is not the first occurrence, then replace it with the new character K, else keep the original character. Also, add the first character of the input string as it is in the beginning.
• Join the resulting list of characters into a single string.
• Print the resulting string.

The original string is : neveropenforLazyroar
Replaced String : Lazyroarfor$eeksfor$eeks

Time Complexity: O(n)

Auxiliary Space: O(n)

Method #5: Using enumeration

1. Initialize the input string test_str and the replacement character K.
2. Initialize an empty string x.
3. Iterate over each character in test_str.
4. If the current character is the same as the first character of the input string and it is not already present in the result string x, append it to x.
5. If the current character is the same as the first character of the input string and it is already present in the result 
6. If the current character is not the same as the first character of the input string, append it to x
7. Print the resulting string

The original string is : neveropenforLazyroar
Replaced String : Lazyroarfor$eeksfor$eeks

Time complexity: The code iterates over the input string once and performs constant time operations for each character. Therefore, the time complexity of the code is O(n), where n is the length of the input string.

Auxiliary Space: The code initializes a string x of the same length as the input string. Therefore, the space complexity of the code is O(n), where n is the length of the input string.