# Python – Alternate Strings Concatenation

• Last Updated : 09 Sep, 2022

The problem of getting concatenation of a list is quite generic and we might some day face the issue of getting the concatenation of alternate elements and get the list of 2 elements containing concatenation of alternate elements. Let’s discuss certain ways in which this can be performed. Method #1 : Using list comprehension + list slicing + join() List slicing clubbed with list comprehension can be used to perform this particular task. We can have list comprehension to get run the logic and list slicing can slice out the alternate character, concat by the join() function.

## Python3

 `# Python3 code to demonstrate``# Alternate Strings Concatenation``# using list comprehension + list slicing` `# initializing list``test_list ``=` `[``"GFG"``, ``"is"``, ``"for"``, ``"Computer"``, ``"Science"``, ``"learning"``]` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))` `# using list comprehension + list slicing``# Alternate Strings Concatenation``res ``=` `[``" "``.join(test_list[i : : ``2``]) ``for` `i ``in` `range``(``len``(test_list) ``/``/``            ``(``len``(test_list)``/``/``2``))]` `# print result``print``(``"The alternate elements concatenation list : "` `+` `str``(res))`

Output :

```The original list : ['GFG', 'is', 'for', 'Computer', 'Science', 'learning']
The alternate elements concatenation list : ['GFG for Science', 'is Computer learning']```

Method #2 : Using loop This is the brute method to perform this particular task in which we have the concatenation of alternate elements in different element indices and then return the output list.

## Python3

 `# Python3 code to demonstrate``# Alternate Strings Concatenation``# using loop` `# initializing list``test_list ``=` `[``"GFG"``, ``"is"``, ``" for"``, ``" Computer"``, ``" Science"``, ``" learning"``]` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))` `# using loop``# Alternate Strings Concatenation``res ``=` `["``", "``"]``for` `i ``in` `range``(``0``, ``len``(test_list)):`` ``if``(i ``%` `2``):``  ``res[``1``] ``+``=` `test_list[i]`` ``else` `:``  ``res[``0``] ``+``=` `test_list[i]` `# print result``print``(``"The alternate elements concatenation list : "` `+` `str``(res))`

Output :

```The original list : ['GFG', 'is', 'for', 'Computer', 'Science', 'learning']
The alternate elements concatenation list : ['GFG for Science', 'is Computer learning']```

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

Time Complexity: O(n)

Auxiliary Space: O(n)

My Personal Notes arrow_drop_up