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# Python | Alternate vowels and consonants in String

Sometimes, while working with Strings in Python, we can have a problem in which we may need restructure a string, adding alternate vowels and consonants in it. This is a popular school-level problem and having solution to this can be useful. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using loop + join() + zip_longest()
The combination of above functions can be used to perform this task. In this, we first, separate vowels and consonants in separate lists. And then join alternatively using zip_longest() and join().

## Python3

 `# Python3 code to demonstrate working of``# Alternate vowels and consonants in String``# using zip_longest() + join() + loop``from` `itertools ``import` `zip_longest` `# initializing string``test_str ``=` `"gaeifgsbou"` `# printing original string``print``(``"The original string is : "` `+` `test_str)` `# Alternate vowels and consonants in String``# using zip_longest() + join() + loop``vowels ``=` `[``'a'``, ``'e'``, ``'i'``, ``'o'``, ``'u'``]``test_vow ``=` `[]``test_con ``=` `[]``for` `ele ``in` `test_str:``   ``if` `ele ``in` `vowels:``       ``test_vow.append(ele)``   ``elif` `ele ``not` `in` `vowels:``       ``test_con.append(ele)``res ``=` `'``'.join('``'.join(ele) for ele in zip_longest(test_vow, test_con, fillvalue ='``'))` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

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

Method #2 : Using loop + map() + lambda
This task can also be performed using combination of above functionalities. It is similar as above method, the only differences are usage of map() and lambda functions to perform alternate joining.

## Python3

 `# Python3 code to demonstrate working of``# Alternate vowels and consonants in String``# using loop + map() + lambda``from` `itertools ``import` `zip_longest` `# initializing string``test_str ``=` `"gaeifgsbou"` `# printing original string``print``(``"The original string is : "` `+` `test_str)` `# Alternate vowels and consonants in String``# using loop + map() + lambda``vowels ``=` `[``'a'``, ``'e'``, ``'i'``, ``'o'``, ``'u'``]``test_vow ``=` `[]``test_con ``=` `[]``for` `ele ``in` `test_str:``   ``if` `ele ``in` `vowels:``       ``test_vow.append(ele)``   ``elif` `ele ``not` `in` `vowels:``       ``test_con.append(ele)``res ``=` `''.join(``map``(``lambda` `sub: sub[``0``] ``+` `sub[``1``],``                  ``zip_longest(test_vow, test_con, fillvalue ``=``'')))` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

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

Method #3: Using regular expression:

## Python3

 `import` `re` `# Initializing string``test_str ``=` `"gaeifgsbou"` `#printing original string``print``(``"The original string is : "` `+` `test_str)`  `# Find all vowels and consonants using regular expressions``vowels ``=` `re.findall(r``'[aeiou]'``, test_str)``consonants ``=` `re.findall(r``'[^aeiou]'``, test_str)` `# Zip the lists together and join the result``result ``=` `''.join([vowel ``+` `consonant ``for` `vowel, consonant ``in` `zip``(vowels, consonants)])` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `result)` `#this code contributed by tvsk`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

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

Method #4: Using operator.countOf() method

## Python3

 `# Python3 code to demonstrate working of``# Alternate vowels and consonants in String``# using operator.countOf() method``from` `itertools ``import` `zip_longest``import` `operator as op``# initializing string``test_str ``=` `"gaeifgsbou"` `# printing original string``print``(``"The original string is : "` `+` `test_str)` `# Alternate vowels and consonants in String``# using operator.countOf() method``vowels ``=` `'aeiouAEIOU'``test_vow ``=` `[]``test_con ``=` `[]``for` `ele ``in` `test_str:``   ``if` `op.countOf(vowels,ele)>``0``:``       ``test_vow.append(ele)``   ``elif` `ele ``not` `in` `vowels:``       ``test_con.append(ele)``res ``=` `'``'.join('``'.join(ele) for ele in zip_longest(test_vow, test_con, fillvalue ='``'))` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

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

Method #5: using for loop and list comprehension

## Python3

 `# initializing string``test_str ``=` `"gaeifgsbou"` `# printing original string``print``(``"The original string is : "` `+` `test_str)` `# Alternate vowels and consonants in String``# using two for loops``vowels ``=` `[``'a'``, ``'e'``, ``'i'``, ``'o'``, ``'u'``]``vowels_list ``=` `[char ``for` `char ``in` `test_str ``if` `char ``in` `vowels]``consonants_list ``=` `[char ``for` `char ``in` `test_str ``if` `char ``not` `in` `vowels]``res ``=` `''``for` `i ``in` `range``(``len``(vowels_list)):``    ``res ``+``=` `vowels_list[i]``    ``if` `i < ``len``(consonants_list):``        ``res ``+``=` `consonants_list[i]` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)``#This code is contributed by Vinay Pinjala.`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

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

Method #6: Using list comprehensions and slicing

Use list comprehensions and slicing to achieve the same result.

Step-by-step approach:

• Initialize two lists, one for vowels and one for consonants.
• Use list comprehension to filter vowels and consonants from the string.
• Use slicing to alternate vowels and consonants.
• Use join() to combine the alternated string.
• Return the alternated string.

Below is the implementation of the above approach:

## Python3

 `# Python3 code to demonstrate working of``# Alternate vowels and consonants in String``# using list comprehension and slicing` `# initializing string``test_str ``=` `"gaeifgsbou"` `# printing original string``print``(``"The original string is : "` `+` `test_str)` `# Alternate vowels and consonants in String``# using list comprehension and slicing``vowels ``=` `[``'a'``, ``'e'``, ``'i'``, ``'o'``, ``'u'``]``test_vow ``=` `[ele ``for` `ele ``in` `test_str ``if` `ele ``in` `vowels]``test_con ``=` `[ele ``for` `ele ``in` `test_str ``if` `ele ``not` `in` `vowels]``res ``=` `''.join([test_vow[i``/``/``2``] ``if` `i``%``2``=``=``0` `else` `test_con[i``/``/``2``] ``for` `i ``in` `range``(``len``(test_str))])` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

Time complexity: O(n)
Auxiliary space: O(n)

Method #7: Using list comprehension and zip()

Use list comprehension and the built-in zip() function to iterate over pairs of consonants and vowels in the string

• initializing string
• printing original string
• Alternate vowels and consonants in String using list comprehension and zip()
• printing result

## Python3

 `# Python3 code to demonstrate working of``# Alternate vowels and consonants in String``# using list comprehension and zip()` `# initializing string``test_str ``=` `"gaeifgsbou"` `# printing original string``print``(``"The original string is : "` `+` `test_str)` `# Alternate vowels and consonants in String``# using list comprehension and zip()``vowels ``=` `[``'a'``, ``'e'``, ``'i'``, ``'o'``, ``'u'``]``consonants ``=` `vowels ``=` `[v ``for` `v ``in` `test_str ``if` `v ``in` `vowels]``res ``=` `''.join([a``+``b ``for` `a,b ``in` `zip``(vowels, consonants)])` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)`

Output

```The original string is : gaeifgsbou
Alternate consonants vowels are: agefigosub```

Time complexity: O(n), where n is the length of the input string.
Auxiliary space: O(n), where n is the length of the input string.

Method #8: Using heapq:

Algorithm:

1. Initialize vowels_list as empty list and consonants_list as empty list
2. For each character ch in test_str, if ch is a vowel, append it to vowels_list, else append it to consonants_list.
3. Sort the vowels_list and consonants_list using heapq.heappush() and heapq.heappop().
4. Initialize an empty string res.
5. For i in range(min(len(vowels_list), len(consonants_list))), append the popped element from vowels_list and consonants_list alternatively to res.
6. Append the remaining elements of vowels_list and consonants_list to res.
7. Print the final res string.

## Python3

 `import` `heapq` `# initializing string``test_str ``=` `"gaeifgsbou"` `# Alternate vowels and consonants in String``# using heapq``vowels ``=` `[``'a'``, ``'e'``, ``'i'``, ``'o'``, ``'u'``]``vowels_list ``=` `[ch ``for` `ch ``in` `test_str ``if` `ch ``in` `vowels]``consonants_list ``=` `[ch ``for` `ch ``in` `test_str ``if` `ch ``not` `in` `vowels]``res ``=` `''.join([heapq.heappop(consonants_list) ``+` `heapq.heappop(vowels_list) ``for` `i ``in` `range``(``min``(``len``(vowels_list), ``len``(consonants_list)))])``res ``+``=` `'``'.join(consonants_list) + '``'.join(vowels_list)` `# printing result``print``(``"Alternate consonants vowels are: "` `+` `res)``#This code is contributed by Rayudu.`

Output

```Alternate consonants vowels are: gabefigosu
```

Time Complexity:
The time complexity of the algorithm is O(nlogn), where n is the length of the input string test_str. This is because the sorting operation in step 3 takes O(nlogn) time.

Space Complexity:
The space complexity of the algorithm is O(n), where n is the length of the input string test_str. This is because we are storing the vowels_list and consonants_list lists which can have a maximum length of n. Additionally, the res string can also have a maximum length of n.

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