Python – Length Conditional Concatenation

Given a list of strings, perform concatenation of Strings whose length is greater than K.

Input : test_list = [“Gfg”, ‘is’, “Best”, ‘for’, ‘CS’, ‘Everything’], K = 3
Output : BestEverything 
Explanation : All elements with Length > 3 are concatenated. 

Input : test_list = [“Gfg”, ‘is’, “Best”, ‘for’, ‘CS’, ‘Everything’], K = 1 
Output : GfgisBestforCSEverything 
Explanation : All elements with Length > 1 are concatenated.

Method #1: Using loop + len():
This offers a brute way to solve this problem. In this, we iterate for each string and perform concatenation if the string length is greater than K using len().

Python3

# Python3 code to demonstrate working of
# Length Conditional Concatenation
# Using loop + len()

# initializing lists
test_list = ["Gfg", 'is', "Best", 'for', 'CS', 'Everything']

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

# initializing K
K = 2

# loop to run through all the elements
res = ''
for ele in test_list:

    # using len() to check for length
    if len(ele) > 2:
        res += ele

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

Output

The original list : ['Gfg', 'is', 'Best', 'for', 'CS', 'Everything']
String after Concatenation : GfgBestforEverything

Time Complexity: O(n)

Auxiliary Space: O(n)

Method #2 : Using join() + filter() + lambda + len():
The combination of above functions can be used to solve this problem. In this, we perform concatenation using join(), filter and lambda are used for conditional check using len().

Python3

# Python3 code to demonstrate working of
# Length Conditional Concatenation
# Using join() + filter() + lambda + len()

# initializing lists
test_list = ["Gfg", 'is', "Best", 'for', 'CS', 'Everything']

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

# initializing K
K = 2

# join() performing Concatenation of required strings
res = ''.join(filter(lambda ele: len(ele) > K, test_list))

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

Output

The original list : ['Gfg', 'is', 'Best', 'for', 'CS', 'Everything']
String after Concatenation : GfgBestforEverything

Time Complexity: O(n)

Auxiliary Space: O(n)

Method#3: Using list comprehension + join():
This method lists strings whose length is greater than the defined number. With the help of join method, we can join the list in string. 

Python3

# Python3 code to demonstrate working of
# Length Conditional Concatenation
# Using list comprehension + join

# Initializing lists
test_list = ["Gfg", 'is', "Best", 'for', 'CS', 'Everything']

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

# Initializing K
K = 3

# list comprehension make list of string with greater length
# join() performing Concatenation of required strings
temp = [x for x in test_list if len(x) > K]
res = "".join(temp)

# Printing result
print("String after Concatenation : " + str(res))

Output

The original list : ['Gfg', 'is', 'Best', 'for', 'CS', 'Everything']
String after Concatenation : BestEverything

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Space Complexity: O(n)

Approach#4: Using reduce

This approach defines a function concat_strings that takes a list test_list and an integer K as input. It uses the filter function with a lambda function to filter the elements of test_list with length greater than K. It then uses the reduce function with a lambda function to concatenate the filtered elements. Finally, it returns the concatenated string.

Algorithm

1. Use reduce function to concatenate the elements of the input list with length greater than K.
2. Return the concatenated string.

Python3

from functools import reduce

def concat_strings(test_list, K):
    filtered_list = filter(lambda string: len(string) > K, test_list)
    concatenated_string = reduce(lambda x, y: x + y, filtered_list, '')
    return concatenated_string
test_list = ["Gfg", 'is', "Best", 'for', 'CS', 'Everything']
K=3
print(concat_strings(test_list, K))

Output

BestEverything

Time Complexity: O(n), where n is the length of the input list.
Auxiliary Space: O(n), where n is the length of the input list (due to the creation of a new iterator).