# Count of adjacent Vowel Consonant Pairs

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 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 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[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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