Replace consonants with next immediate consonants alphabetically in a String

Given a string which contains lowercase English alphabets. The task is to replace each consonant with the next immediate consonant that comes in English alphabets.
Let's say we have to replace character , it will be replaced by . Another example, let's say we have to replace character , the next immediate consonant is , hence will be replaced by .

Note: If the character is 'z', then look circularly in English alphabets for the next consonant, i.e. replace it with 'b'.

Examples: 

Input : str = "geeksforgeeks"
Output : heeltgosheelt

Input : str = "gfg"
Output : hgh

Approach: 

• Iterate the string elements from left to right.
• If the string element is consonant, then check the next immediate alphabet of this element.
• If the next immediate alphabet is a consonant, then replace it with the this alphabet. If it is a vowel, then replace the string element with 2nd immediate alphabet as there are no consecutive vowels in English alphabets.

Below is the implementation of the above program: 

heeltgosheelt

Complexity Analysis:

• Time Complexity: O(n), where n is the size of string s 
• Auxiliary Space: O(1)