Python – Replace to K at ith Index in String

Given a String, replace ith index by K value.

Input : test_str = 'Lazyroar5Lazyroar', K = '7', i = 5 
Output : 'Lazyroar7Lazyroar' 
Explanation : Element is 5, converted to 7 on ith index. 

Input : test_str = 'Lazyroar5Lazyroar', K = '7', i = 6 
Output : 'Lazyroar56eeks' 
Explanation : Element is g, converted to 7 on ith index.

Method #1: Using string slicing

In this, we perform the slicing of pre string, till i, and then add K, then add post values, using string slice method.

The original string is : Lazyroar5Lazyroar
The constructed string : Lazyroar4Lazyroar

Time Complexity: O(n) -> string slicing
Auxiliary Space: O(n)

Method #2 : Using join() + generator expression

In this, we perform the task of checking for ith index and conditionally appending K, using generator expression and convert the result into string using join().

The original string is : Lazyroar5Lazyroar
The constructed string : Lazyroar4Lazyroar

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

Method #3 : Using replace() method

The original string is : Lazyroar5Lazyroar
The constructed string : Lazyroar4Lazyroar

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

Method #4 : Using list() and join() methods

The original string is : Lazyroar5Lazyroar
The constructed string : Lazyroar4Lazyroar

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

Method #5: Using bytearray()

1. Initialize the string test_str and print it.
2. Initialize the values of K and i.
3. Convert the string to a bytearray using bytearray(test_str, encoding=’utf-8′). This creates a mutable bytearray object that can be modified in-place.
4. Replace the character at index i with K by assigning K to test_str[i].
5. Convert the bytearray back to a string using bytes.decode() method.
6. Print the resulting string.

The original string is : Lazyroar5Lazyroar
The constructed string : Lazyroar4Lazyroar

Time complexity: O(n), where n is the length of the input string.
Auxiliary space: O(n), where n is the length of the input string.

Method #6: Using string concatenation and string indexing

Step-by-step approach:

• Initialize the original string, K, and i variables.
• Create a new string variable to store the modified string.
• Loop through each character in the original string, adding each character to the new string until you reach the index i.
  • Add the character K to the new string.
  • Continue looping through the original string, starting at the index i+1, and adding each character to the new string.
• Print the new string.

Below is the implementation of the above approach:

The original string is : Lazyroar5Lazyroar
The constructed string : Lazyroar4Lazyroar

Time complexity: O(n), where n is the length of the original string.
Auxiliary space: O(n), where n is the length of the original string, since we are creating a new string to store the modified string.