Length of the longest substring consisting only of vowels in non-increasing order

Given a string S of size N consisting of lowercase alphabets, the task is to print the length of the longest substring consisting only of vowels sorted in non-increasing order.

Examples:

Input: S = “ueiaoaeiouuoiea”
Output: 6
Explanation: The only substring which consists only of vowels in non-increasing order, is the substring {S[9], S[15]}, which is “uuoiea”.

Input: S = “uuuioea”
Output: 0

Approach: The given problem can be solved using HashSet. Follow the steps below to solve the problem:

• Store all the vowels in an array, say ch[], in decreasing order.
• Initialize three variables res, j, and count as 0, to store the longest length of the required substring, to iterate over all vowels, and to store the length of the current substring satisfying the conditions respectively.
• Also, initialize a HashSet say mp to store all the distinct characters of the current substring satisfying the conditions.
• Iterate over the characters of the string S using a variable i and perform the following operations:
  • If S[i] is equal to ch[j] then add S[i] to mp and then increment j and count by 1. If the size of mp is equal to 5, then update res to a maximum of res and count.
  • Otherwise, if j + 1 is less than 5 and S[i] is equal to ch[j + 1], then increment j and count by 1 and add S[i] to mp. If the size of mp is equal to 5, then update res to a maximum of res and count.
  • Otherwise, if S[i] is equal to ‘u‘ then assign 0 to j and 1 to count and add S[i] to mp. Otherwise, assign 0 to both j and count.
• After completing the above steps, print the value of res as the result.

Below is the implementation of the above approach:

C++

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to find length of the
// longest substring consisting only
// of vowels in non-increasing order
int count(string S, int N)
{

    // Stores all vowels in decreasing order
    char ch[] = { 'u', 'o', 'i', 'e', 'a' };

    // Stores current index of array ch[]
    int j = 0;

    // Stores the result
    int res = 0;

    // Stores the count
    // of current substring
    int count = 0;

    // Declare a HashSet to store the vowels
    unordered_set<char> mp;

    // Traverse the string, S
    for(int i = 0; i < N; ++i)
    {

        // If S[i] is equal to ch[j]
        if (S[i] == ch[j])
        {

            // Increment count by 1
            ++count;

            // Add S[i] in the mp
            mp.insert(S[i]);

            // If length of mp is 5, update res
            if (mp.size() == 5)
            {
                res = max(res, count);
            }
        }

        // Else if j+1 is less than 5 and
        // S[i] is equal to ch[j+1]
        else if (j + 1 < 5 && S[i] == ch[j + 1])
        {

            // Add the S[i] in the mp
            mp.insert(S[i]);

            // Increment count by 1
            ++count;

            // Increment j by 1
            j++;

            // If length of mp is 5, update res
            if (mp.size() == 5)
            {
                res = max(res, count);
            }
        }
        else
        {

            // Clear the mp
            mp.clear();

            // If S[i] is 'u'
            if (S[i] == 'u')
            {

                // Add S[i] in the mp
                mp.insert('u');

                // Update j and assign 1 to count
                j = 0;
                count = 1;
            }

            // Else assign 0 to j and count
            else
            {
                j = 0;
                count = 0;
            }
        }
    }

    // Return the result
    return res;
}

// Driver Code
int main()
{
    string S = "ueiaoaeiouuoiea";
    int N = S.size();

    // Function Call
    cout << count(S, N);

    return 0;
}

// This code is contributed by Kingash

Java

// Java program for the above approach
import java.io.*;
import java.util.*;

class GFG {

    // Function to find length of the
    // longest substring consisting only
    // of vowels in non-increasing order
    static int count(String S, int N)
    {

        // Stores all vowels in decreasing order
        char ch[] = { 'u', 'o', 'i', 'e', 'a' };

        // Stores current index of array ch[]
        int j = 0;

        // Stores the result
        int res = 0;

        // Stores the count
        // of current substring
        int count = 0;

        // Declare a HashSet to store the vowels
        HashSet<Character> mp = new HashSet<>();

        // Traverse the string, S
        for (int i = 0; i < N; ++i) {

            // If S[i] is equal to ch[j]
            if (S.charAt(i) == ch[j]) {

                // Increment count by 1
                ++count;

                // Add S[i] in the mp
                mp.add(S.charAt(i));

                // If length of mp is 5, update res
                if (mp.size() == 5) {
                    res = Math.max(res, count);
                }
            }

            // Else if j+1 is less than 5 and
            // S[i] is equal to ch[j+1]
            else if (j + 1 < 5
                     && S.charAt(i) == ch[j + 1]) {

                // Add the S[i] in the mp
                mp.add(S.charAt(i));

                // Increment count by 1
                ++count;

                // Increment j by 1
                j++;

                // If length of mp is 5, update res
                if (mp.size() == 5) {
                    res = Math.max(res, count);
                }
            }
            else {

                // Clear the mp
                mp.clear();

                // If S[i] is 'u'
                if (S.charAt(i) == 'u') {

                    // Add S[i] in the mp
                    mp.add('u');

                    // Update j and assign 1 to count
                    j = 0;
                    count = 1;
                }

                // Else assign 0 to j and count
                else {
                    j = 0;
                    count = 0;
                }
            }
        }

        // Return the result
        return res;
    }

    // Driver Code
    public static void main(String[] args)
    {

        // Given Input
        String S = "ueiaoaeiouuoiea";
        int N = S.length();

        // Function Call
        System.out.println(count(S, N));
    }
}

Python3

# Python3 program for the above approach

# Function to find length of the
# longest substring consisting only
# of vowels in non-increasing order
def count1(S, N):

    # Stores all vowels in decreasing order
    ch = ['u', 'o', 'i', 'e', 'a']

    # Stores current index of array ch[]
    j = 0

    # Stores the result
    res = 0

    # Stores the count
    # of current substring
    count = 0;

    # Declare a HashSet to store the vowels
    mp = set()

    # Traverse the string, S
    for i in range(N):

        # If S[i] is equal to ch[j]
        if (S[i] == ch[j]):

            # Increment count by 1
            count += 1

            # Add S[i] in the mp
            mp.add(S[i])

            # If length of mp is 5, update res
            if (len(mp) == 5):
                res = max(res, count)

        # Else if j+1 is less than 5 and
        # S[i] is equal to ch[j+1]
        elif (j + 1 < 5 and S[i] == ch[j + 1]):

            # Add the S[i] in the mp
            mp.add(S[i])

            # Increment count by 1
            count += 1

            # Increment j by 1
            j += 1

            # If length of mp is 5, update res
            if (len(mp) == 5):
                res = max(res, count)
        else:

            # Clear the mp
            mp.clear()

            # If S[i] is 'u'
            if (S[i] == 'u'):

                # Add S[i] in the mp
                mp.add('u')

                # Update j and assign 1 to count
                j = 0
                count = 1

            # Else assign 0 to j and count
            else:
                j = 0
                count = 0

    # Return the result
    return res

# Driver Code
if __name__ == '__main__':

    S = "ueiaoaeiouuoiea"
    N = len(S)

    # Function Call
    print(count1(S, N))

# This code is contributed by SURENDRA_GANGWAR

C#

// C# program for the above approach
using System;
using System.Collections.Generic;
class GFG {

  // Function to find length of the
  // longest substring consisting only
  // of vowels in non-increasing order
  static int count(string S, int N)
  {

    // Stores all vowels in decreasing order
    char[] ch = { 'u', 'o', 'i', 'e', 'a' };

    // Stores current index of array ch[]
    int j = 0;

    // Stores the result
    int res = 0;

    // Stores the count
    // of current substring
    int count = 0;

    // Declare a HashSet to store the vowels
    HashSet<char> mp = new HashSet<char>();

    // Traverse the string, S
    for (int i = 0; i < N; ++i) {

      // If S[i] is equal to ch[j]
      if (S[i] == ch[j]) {

        // Increment count by 1
        ++count;

        // Add S[i] in the mp
        mp.Add(S[i]);

        // If length of mp is 5, update res
        if (mp.Count == 5) {
          res = Math.Max(res, count);
        }
      }

      // Else if j+1 is less than 5 and
      // S[i] is equal to ch[j+1]
      else if (j + 1 < 5 && S[i] == ch[j + 1]) {

        // Add the S[i] in the mp
        mp.Add(S[i]);

        // Increment count by 1
        ++count;

        // Increment j by 1
        j++;

        // If length of mp is 5, update res
        if (mp.Count == 5) {
          res = Math.Max(res, count);
        }
      }
      else {

        // Clear the mp
        mp.Clear();

        // If S[i] is 'u'
        if (S[i] == 'u') {

          // Add S[i] in the mp
          mp.Add('u');

          // Update j and assign 1 to count
          j = 0;
          count = 1;
        }

        // Else assign 0 to j and count
        else {
          j = 0;
          count = 0;
        }
      }
    }

    // Return the result
    return res;
  }

  // Driver Code
  public static void Main(string[] args)
  {

    // Given Input
    string S = "ueiaoaeiouuoiea";
    int N = S.Length;

    // Function Call
    Console.WriteLine(count(S, N));
  }
}

// This code is contributed by ukasp.

Javascript

<script>

// Javascript program for the above approach

// Function to find length of the
// longest substring consisting only
// of vowels in non-increasing order
function count(S, N)
{

    // Stores all vowels in decreasing order
    let ch = [ 'u', 'o', 'i', 'e', 'a' ];

    // Stores current index of array ch[]
    let j = 0;

    // Stores the result
    let res = 0;

    // Stores the count
    // of current substring
    let count = 0;

    // Declare a HashSet to store the vowels
    let mp = new Map();

    // Traverse the string, S
    for(let i = 0; i < N; ++i)
    {

        // If S[i] is equal to ch[j]
        if (S[i] == ch[j])
        {

            // Increment count by 1
            ++count;

            // Add S[i] in the mp
            mp.set(S[i], "");

            // If length of mp is 5, update res
            if (mp.size == 5)
            {
                res = Math.max(res, count);
            }
        }

        // Else if j+1 is less than 5 and
        // S[i] is equal to ch[j+1]
        else if (j + 1 < 5 && S[i] == ch[j + 1])
        {

            // Add the S[i] in the mp
            mp.set(S[i], "");

            // Increment count by 1
            ++count;

            // Increment j by 1
            j++;

            // If length of mp is 5, update res
            if (mp.size == 5)
            {
                res = Math.max(res, count);
            }
        }
        else
        {

            // Clear the mp
            mp.clear();

            // If S[i] is 'u'
            if (S[i] == 'u')
            {

                // Add S[i] in the mp
                mp.set('u', "");

                // Update j and assign 1 to count
                j = 0;
                count = 1;
            }

            // Else assign 0 to j and count
            else
            {
                j = 0;
                count = 0;
            }
        }
    }

    // Return the result
    return res;
}

// Driver Code
let S = "ueiaoaeiouuoiea";
let N = S.length;

// Function Call
document.write(count(S, N));

// This code is contributed by _saurabh_jaiswal

</script>

Output:

6

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