Python Program to Reverse consonants in a given string without affecting the other elements

Given a string, the task is to write a Python program to reverse only the consonants of a string without affecting the other elements’ positions.

Examples:

Input : hello

Output : lelho

Explanation: h,l,l are consonants in the given string. After modifying the string their occurrences are l,l,h and vowels positions are not changed.

Approach:

• Convert the string into a list of characters.
• Maintain another Python list for storing consonants.
• If the current element is consonant then append the current element to the consonant list.
• Start traversing the list again and replace the consonants with the element present in the consonant list from last.
• Finally, convert the list into a string and return it.

Implementation

Below is the implementation of the above approach.

Python3

# Function to check element is consonant or not
def isConsonant(i):
    vow = ['a', 'e', 'i', 'o', 'u']

    # if not vowel return true
    if i not in vow:
        return True
    return False


def reverseConsonant(s):

    # convert string into list
    s = list(s)

    # storing consonants in a list
    cons = []
    for i in s:
        if isConsonant(i):
            cons.append(i)
    k = len(cons)-1

    # Replace the consonants with the
    # element present in consonant list
    # from last.
    for i in range(len(s)):
        if isConsonant(s[i]):
            s[i] = cons[k]
            k -= 1
    return "".join(s)

print(reverseConsonant("hello world"))
print(reverseConsonant("bcdfghjklm"))

Output:

delrow ollh
mlkjhgfdcb

Complexity Analysis

Time complexity: O(n)

Space Complexity: O(n) for storing consonants