Python – Remove strings with any non-required character

Given a Strings list, remove string, if it contains any unwanted character.

Input : test_list = [“gfg”, “is”, “best”, “for”, “geeks”], chr_list = [‘f’, ‘m’, ‘n’, ‘i’] 
Output : [‘best’, ‘geeks’] 
Explanation : Given Strings don’t contain f, m, n or i.

Input : test_list = [“gfg”, “is”, “best”, “for”, “geeks”], chr_list = [‘f’, ‘m’, ‘n’] 
Output : [‘best’, ‘geeks’, ‘is’] 
Explanation : Given Strings don’t contain f, m or n. 

Method #1 : Using list comprehension + any()

In this, we test all strings and use any() to iterate all the non-required characters list and check its presence in string, if found, that list is not included in result list.

Python3

# Python3 code to demonstrate working of
# Remove strings with any non-required character
# Using list comprehension + any()

# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]

# printing original list
print("The original list is : " + str(test_list))

# non-required char list
chr_list = ['f', 'm', 'n', 'i']

# checking for all strings
# removing if contains even 1 character
res = [sub for sub in test_list if not any(ele in sub for ele in chr_list)]

# printing result
print("Filtered Strings : " + str(res))

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeks']
Filtered Strings : ['best', 'geeks']

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

Method #2 : Using filter() + lambda + any()

In this, we perform task of filtering using filter() and lambda function. Rest any() is used to check for any character present in strings for its removal.

Python3

# Python3 code to demonstrate working of
# Remove strings with any non-required character
# Using filter() + lambda + any()

# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]

# printing original list
print("The original list is : " + str(test_list))

# non-required char list
chr_list = ['f', 'm', 'n', 'i']

# checking for all strings
# filter and lambda used to do this task
res = list(filter(lambda sub: not any(
    ele in sub for ele in chr_list), test_list))

# printing result
print("Filtered Strings : " + str(res))

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeks']
Filtered Strings : ['best', 'geeks']

Time Complexity: O(n) where n is the number of elements in the list “test_list”.  filter() and lambda function performs n number of operations.
Auxiliary Space: O(1), no extra space is required

Method #3 : Using replace() method

Python3

# Python3 code to demonstrate working of
# Remove strings with any non-required character

# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]

# printing original list
print("The original list is : " + str(test_list))

# non-required char list
chr_list = ['f', 'm', 'n', 'i']

# checking for all strings
x=[]
for i in test_list:
    for j in chr_list:
        i=i.replace(j,"")
    x.append(i)
res=[]
for i in range(0,len(test_list)):
    if(test_list[i]==x[i]):
        res.append(test_list[i])
# printing result
print("Filtered Strings : " + str(res))

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeks']
Filtered Strings : ['best', 'geeks']

Method#4: Using Recursive method.

Algorithm:

1. Define a function remove_strings that takes a list of strings lst and a list of non-required characters chr_list as input.
2. Check if the input list lst is empty, if yes then return an empty list.
3. Otherwise, get the first string in the input list lst.
4. Recursively call the remove_strings function on the rest of the input list lst.
5. Check if the first string first contains any non-required character from the chr_list.
6. If yes, exclude the string first from the result and return the remaining modified list rest.
7. If no, include the string first in the result and return the modified list rest with first added to the front.

Python3

# Python3 code to demonstrate working of
# Remove strings with any non-required character
# Using recursive method
def remove_strings(lst, chr_list):
    if not lst:  # base case for empty list
        return []
    else:
        # get the first string in the list
        first = lst[0]

        # recursively remove strings from the rest of the list
        rest = remove_strings(lst[1:], chr_list)

        # check if the first string contains any non-required character
        if any(ele in first for ele in chr_list):
            # if yes, don't include it in the result
            return rest
        else:
            # otherwise, include it in the result
            return [first] + rest

# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]

# printing original list
print("The original list is : " + str(test_list))

# non-required char list
chr_list = ['f', 'm', 'n', 'i']

# checking for all strings
# removing if contains even 1 character
res = remove_strings(test_list,chr_list)
# printing result
print("Filtered Strings : " + str(res))

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeks']
Filtered Strings : ['best', 'geeks']

The time complexity of this algorithm is O(nmk), where n is the length of the input list lst, m is the average length of the strings in lst, and k is the length of the chr_list. This is because we are looping through the input list lst once, and for each string in lst, we are checking for the presence of any non-required character from chr_list, which takes O(mk) time. 

The auxiliary space of this algorithm is also O(nm), because we are creating a new list of modified strings of the same length as the input list. However, this algorithm has a recursive structure, so it may use additional space on the call stack.