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Count of adjacent Vowel Consonant Pairs
• Last Updated : 02 Jun, 2021

Given a string, the task is to count the number of adjacent pairs such that the first element of the pair is a consonant and the second element is a vowel. That is find the number of pairs (i, i+1) such that the ith character of this string is a consonant and the (i+1)th character is a vowel.
Examples:

```Input :  str = "bazeci"
Output : 3

Input : str = "abu"
Output : 1```

Algorithm

1. We have to find all possible adjacent consonant-vowel pairs.
2. Insert all of the vowels in a set or hash, so that we can check if the current character is a vowel or consonant in constant time.
3. We run a loop for the first n-1 elements and check, if the ith character is a consonant, and the (i+1)th character a vowel or not.
4. If so, we increment the count, else we continue till the end of the string.

Below is the implementation of the above approach:

## C++

 `// C++ Program to implement the above approach` `#include ``using` `namespace` `std;` `// Function to count the adjacent pairs of``// consonant and vowels in the string``int` `countPairs(string s)``{``    ``// Using a set to store the vowels so that``    ``// checking each character becomes easier``    ``set<``char``> st;``    ``st.insert(``'a'``);``    ``st.insert(``'e'``);``    ``st.insert(``'i'``);``    ``st.insert(``'o'``);``    ``st.insert(``'u'``);` `    ``// Variable to store number of``    ``// consonant-vowel pairs``    ``int` `count = 0;` `    ``int` `n = s.size();` `    ``for` `(``int` `i = 0; i < n - 1; i++) {` `        ``// If the ith character is not found in the set,``        ``// means it is a consonant``        ``// And if the (i+1)th character is found in the set,``        ``// means it is a vowel``        ``// We increment the count of such pairs``        ``if` `(st.find(s[i]) == st.end() && st.find(s[i + 1]) != st.end())``            ``count++;``    ``}` `    ``return` `count;``}` `// Driver Code``int` `main()``{``    ``string s = ``"geeksforgeeks"``;` `    ``cout << countPairs(s);` `    ``return` `0;``}`

## Java

 `// Java Program to implement the above approach``import` `java.util.*;` `class` `Sol``{``    ` `// Function to count the adjacent pairs of``// consonant and vowels in the String``static` `int` `countPairs(String s)``{``    ``// Using a set to store the vowels so that``    ``// checking each character becomes easier``    ``Set st=``new` `HashSet();``    ``st.add(``'a'``);``    ``st.add(``'e'``);``    ``st.add(``'i'``);``    ``st.add(``'o'``);``    ``st.add(``'u'``);` `    ``// Variable to store number of``    ``// consonant-vowel pairs``    ``int` `count = ``0``;` `    ``int` `n = s.length();` `    ``for` `(``int` `i = ``0``; i < n - ``1``; i++)``    ``{` `        ``// If the ith character is not found in the set,``        ``// means it is a consonant``        ``// And if the (i+1)th character is found in the set,``        ``// means it is a vowel``        ``// We increment the count of such pairs``        ``if` `(st.contains(s.charAt(i)) && !st.contains(s.charAt(i + ``1``)))``            ``count++;``    ``}` `    ``return` `count;``}` `// Driver Code``public` `static` `void` `main(String args[])``{``    ``String s = ``"geeksforgeeks"``;` `    ``System.out.println( countPairs(s));``}``}` `// This code is contributed by Arnab Kundu`

## Python3

 `# Python3 Program to implement the above approach` `# Function to count the adjacent pairs of``# consonant and vowels in the string``def` `countPairs(s) :` `    ``# Using a set to store the vowels so that``    ``# checking each character becomes easier``    ``st ``=` `set``();``    ``st.add(``'a'``);``    ``st.add(``'e'``);``    ``st.add(``'i'``);``    ``st.add(``'o'``);``    ``st.add(``'u'``);` `    ``# Variable to store number of``    ``# consonant-vowel pairs``    ``count ``=` `0``;` `    ``n ``=` `len``(s);` `    ``for` `i ``in` `range``(n ``-` `1``) :``        ` `        ``# If the ith character is not found in the set,``        ``# means it is a consonant``        ``# And if the (i+1)th character is found in the set,``        ``# means it is a vowel``        ``# We increment the count of such pairs``        ``if` `(s[i] ``not` `in` `st ``and` `s[i ``+` `1``] ``in` `st) :``            ``count ``+``=` `1``;` `    ``return` `count;` `# Driver Code``if` `__name__ ``=``=` `"__main__"` `:``    ` `    ``s ``=` `"geeksforgeeks"``;` `    ``print``(countPairs(s));``    ` `# This code is contributed by AnkitRai01`

## C#

 `// C# implementation of the approach``using` `System;``using` `System.Collections.Generic;` `class` `GFG``{``    ` `// Function to count the adjacent pairs of``// consonant and vowels in the String``static` `int` `countPairs(String s)``{``    ``// Using a set to store the vowels so that``    ``// checking each character becomes easier``    ``HashSet<``char``> st = ``new` `HashSet<``char``>();``    ``st.Add(``'a'``);``    ``st.Add(``'e'``);``    ``st.Add(``'i'``);``    ``st.Add(``'o'``);``    ``st.Add(``'u'``);` `    ``// Variable to store number of``    ``// consonant-vowel pairs``    ``int` `count = 0;` `    ``int` `n = s.Length;` `    ``for` `(``int` `i = 0; i < n - 1; i++)``    ``{` `        ``// If the ith character is not found in the set,``        ``// means it is a consonant``        ``// And if the (i+1)th character is found in the set,``        ``// means it is a vowel``        ``// We increment the count of such pairs``        ``if` `(st.Contains(s[i]) && !st.Contains(s[i + 1]))``            ``count++;``    ``}` `    ``return` `count;``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``String s = ``"geeksforgeeks"``;` `    ``Console.Write( countPairs(s));``}``}` `// This code has been contributed by 29AjayKumar`

## Javascript

 ``
Output:

`3`

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(1). We have used additional space to store vowels in a Hash but since number of vowels is only 5 so, the extra space used is considered as constant.

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