Given a String List and order list, perform string concatenation in a specific order.
Input : test_list = [“best”, “Gfg”, “for”, “is”], sort_order = [1, 3, 0, 2]
Output : Gfgisbestfor
Explanation : Combined as per order of indices.Input : test_list = [“best”, “Gfg”], sort_order = [1, 0]
Output : Gfgbest
Explanation : Combined as per order of indices.
Method #1: Using loop
In this, we iterate order elements in the loop and perform concatenation of strings of the similar index in similar order.
Python3
# Python3 code to demonstrate working of # Concatenate Strings in Order# Using loop# initializing listtest_list = ["best", "Gfg", "for", "is", "Lazyroar"]# printing original listprint("The original list is : " + str(test_list))# initializing join order sort_order = [1, 3, 0, 2, 4]res = ''for order in sort_order: # concatenating by order res += test_list[order]# printing result print("Ordered concatenation : " + str(res)) |
The original list is : ['best', 'Gfg', 'for', 'is', 'Lazyroar'] Ordered concatenation : GfgisbestforLazyroar
Time Complexity: O(n) where n is the number of elements in the list “test_list”.
Auxiliary Space: O(1) additional space is not needed
Method #2: Using join() + list comprehension
In this, we perform the task of concatenation using join(), list comprehension is used for iteration of order.
Python3
# Python3 code to demonstrate working of # Concatenate Strings in Order# Using join() + list comprehension# initializing listtest_list = ["best", "Gfg", "for", "is", "Lazyroar"]# printing original listprint("The original list is : " + str(test_list))# initializing join order sort_order = [1, 3, 0, 2, 4]# join() performs concatenationres = ''.join([test_list[order] for order in sort_order])# printing result print("Ordered concatenation : " + str(res)) |
The original list is : ['best', 'Gfg', 'for', 'is', 'Lazyroar'] Ordered concatenation : GfgisbestforLazyroar
Time Complexity: O(n)
Space Complexity: O(n)
Method #3: Using map()
Here’s a different approach, which leverages the python map() function:
Python3
# Python3 code to demonstrate working of# Concatenate Strings in Order# Using map()# initializing listtest_list = ["best", "Gfg", "for", "is", "Lazyroar"]# printing original listprint("The original list is : " + str(test_list))# initializing join ordersort_order = [1, 3, 0, 2, 4]# using map() to get the concatenated stringres = ''.join(map(lambda x: test_list[x], sort_order))# printing resultprint("Ordered concatenation : " + str(res)) |
The original list is : ['best', 'Gfg', 'for', 'is', 'Lazyroar'] Ordered concatenation : GfgisbestforLazyroar
Time Complexity: O(n)
Auxiliary Space: O(n)
The code leverages the map() function to iterate over the sort_order list, and using a lambda function, it retrieves the corresponding string from the test_list. The join() function is then used to concatenate the retrieved strings into a single string.
Method 4: Using the zip() function and a generator expression
Step-by-step approach:
- The program begins by initializing a list named test_list with some strings.
- The print() function is used to display the original list.
- Next, another list named sort_order is initialized with a specific order in which the strings need to be concatenated.
- The zip() function is then used to map the values of test_list and sort_order together.
- A generator expression is used to iterate over the mapped values, where each value represents the index of the element in test_list in the order specified in sort_order.
- The join() function is then used to concatenate the strings in the order specified by the sort_order list.
- The final concatenated string is stored in a variable named res.
- Finally, the concatenated string is displayed using the print() function.
Python3
# Python3 code to demonstrate working of # Concatenate Strings in Order# Using zip() + generator expression # initializing listtest_list = ["best", "Gfg", "for", "is", "Lazyroar"]# printing original listprint("The original list is : " + str(test_list))# initializing join order sort_order = [1, 3, 0, 2, 4]# using zip() to map values# iterating over the generator expressionres = ''.join(test_list[i] for i in sort_order)# printing result print("Ordered concatenation : " + str(res)) |
The original list is : ['best', 'Gfg', 'for', 'is', 'Lazyroar'] Ordered concatenation : GfgisbestforLazyroar
Time complexity: O(n), where n is the length of the list and the sort_order array. Both of these are iterated over once.
Auxiliary space: O(1), since we only use constant extra space to store the intermediate result and no additional data structures are used
Method 5: Use the sorted() function with a custom key function.
Step-by-step approach:
- Initialize the list of strings.
- Initialize the order of concatenation.
- Define a custom key function that returns the index of the current string in the sort_order list.
- Use the sorted() function with the key function to sort the list of strings in the given order.
- Join the sorted list of strings using the join() method.
- Print the final result.
Python3
# Python3 code to demonstrate working of# Concatenate Strings in Order# Using sorted() function with custom key# initializing listtest_list = ["best", "Gfg", "for", "is", "Lazyroar"]# printing original listprint("The original list is : " + str(test_list))# initializing join ordersort_order = [1, 3, 0, 2, 4]# define a custom key functiondef custom_key(item): return sort_order.index(test_list.index(item))# using sorted() with custom key to concatenate strings in orderres = ''.join(sorted(test_list, key=custom_key))# printing resultprint("Ordered concatenation : " + str(res)) |
The original list is : ['best', 'Gfg', 'for', 'is', 'Lazyroar'] Ordered concatenation : GfgisbestforLazyroar
Time complexity: O(nlogn) due to the use of sorted(),
Auxiliary space: O(n) for storing the sorted list of strings.
