Python – Remove N characters after K

Given a String, remove N characters after K character.

Input : test_str = ‘ge@987eksfor@123geeks is best@212 for cs’, N = 3, K = ‘@’ Output : ‘geeksforgeeks is best for cs’ Explanation : All 3 required occurrences removed. Input : test_str = ‘geeksfor@123geeks is best for cs’, N = 3, K = ‘@’ Output : ‘geeksforgeeks is best for cs’ Explanation : @123 is removed.

Method #1 : Using re.sub()

In this, we specify appropriate regex to capture the element and to remove next N occurrences from String. The sub() is used to perform replacement.

Python3

# Python3 code to demonstrate working of
# Remove N characters after K
# Using re.sub()
import re

# initializing strings
test_str = 'geeksfor@123geeks is best@212 for cs'

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

# initializing N
N = 3

# initializing K
K = '@'

# using re.sub() to perform task
res = re.sub(r'\@...', '', test_str)

# printing result
print("The String after removal : " + str(res))

Output

The original string is : geeksfor@123geeks is best@212 for cs
The String after removal : geeksforgeeks is best for cs

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

Method #2 : Using re.sub() + occurrence option

This is similar to above, just using 4th argument of re.sub() to control the occurrence counts we wish to perform replace.

Python3

# Python3 code to demonstrate working of
# Remove N characters after K
# Using re.sub() + occurrence option
import re

# initializing strings
test_str = 'geeksfor@123geeks is best@212 for cs'

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

# initializing N
N = 3

# initializing K
K = '@'

# using re.sub() to perform task
# controlling occurrence using 4th arg.
# removes just 1st occurrence
res = re.sub(r'\@...', '', test_str, 1)

# printing result
print("The String after removal : " + str(res))

Output

The original string is : geeksfor@123geeks is best@212 for cs
The String after removal : geeksforgeeks is best@212 for cs

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

Time Complexity: O(n)

Space Complexity: O(n)