Longest Subsequence of a String containing only vowels

Given a string str containing only alphabets, the task is to print the longest subsequence of the string str containing only vowels.
Examples:

Input: str = “geeksforgeeks” 
Output: eeoee 
Explanation:
“eeoee” is the longest subsequence of the string containing only vowels. 
Input: str = “HelloWorld” 
Output: eoo 
Explanation:
“eeo” is the longest subsequence of the string containing only vowels. 

Approach:

• Traverse through the given string character by character.
• If the character is a vowel, append it to the resultant string.
• When the traversal completes, the required longest subsequence containing only vowels is stored in the resultant string.

Below is the implementation of the above approach: 

C++

// C++ program to find the longest
// subsequence containing only vowels

#include <bits/stdc++.h>
using namespace std;

// Function to check whether
// a character is vowel or not
bool isVowel(char x)
{
    x = tolower(x);

    // Returns true if x is vowel
    return (x == 'a' || x == 'e'
            || x == 'i' || x == 'o'
            || x == 'u');
}

// Function to find the longest subsequence
// which contain all vowels
string longestVowelSubsequence(string str)
{
    string answer = "";

    // Length of the string
    int n = str.size();

    // Iterating through the string
    for (int i = 0; i < n; i++) {

        // Checking if the character is a
        // vowel or not
        if (isVowel(str[i])) {

            // If it is a vowel, then add it
            // to the final string
            answer += str[i];
        }
    }

    return answer;
}

// Driver code
int main()
{
    string str = "geeksforgeeks";
    cout << longestVowelSubsequence(str)
 << endl;

    return 0;
}

Java

// Java program to find the longest
// subsequence containing only vowels
class GFG{

// Function to check whether
// a character is vowel or not
static boolean isVowel(char x)
{
    x = Character.toLowerCase(x);

    // Returns true if x is vowel
    return (x == 'a' || x == 'e'
            || x == 'i' || x == 'o'
            || x == 'u');
}

// Function to find the longest subsequence
// which contain all vowels
static String longestVowelSubsequence(String str)
{
    String answer = "";

    // Length of the String
    int n = str.length();

    // Iterating through the String
    for (int i = 0; i < n; i++) {

        // Checking if the character is a
        // vowel or not
        if (isVowel(str.charAt(i))) {

            // If it is a vowel, then add it
            // to the final String
            answer += str.charAt(i);
        }
    }
    return answer;
}

// Driver code
public static void main(String[] args)
{
    String str = "geeksforgeeks";
    System.out.print(longestVowelSubsequence(str)
 +"\n");
}
}

// This code is contributed by 29AjayKumar

Python 3

# Python 3 program to find the longest
# subsequence containing only vowels

# Function to check whether
# a character is vowel or not
def isVowel(x):

    # Returns true if x is vowel
    return (x == 'a' or x == 'e'or x == 'i' or x == 'o' or x == 'u')

# Function to find the longest subsequence
# which contain all vowels
def longestVowelSubsequence(str):

    answer = ""

    # Length of the string
    n = len(str)

    # Iterating through the string
    for i in range(n):

        # Checking if the character is a
        # vowel or not
        if (isVowel(str[i])):

            # If it is a vowel, then add it
            # to the final string
            answer += str[i]

    return answer

# Driver code
str = "geeksforgeeks"
print(longestVowelSubsequence(str))

# This code is contributed by apurva raj

C#

// C# program to find the longest
// subsequence containing only vowels
using System;

class GFG{

// Function to check whether
// a character is vowel or not
static bool isVowel(char x)
{
    x = char.ToLower(x);

    // Returns true if x is vowel
    return (x == 'a' || x == 'e'
            || x == 'i' || x == 'o'
            || x == 'u');
}

// Function to find the longest subsequence
// which contain all vowels
static String longestVowelSubsequence(String str)
{
    String answer = "";

    // Length of the String
    int n = str.Length;

    // Iterating through the String
    for (int i = 0; i < n; i++) {

        // Checking if the character is a
        // vowel or not
        if (isVowel(str[i])) {

            // If it is a vowel, then add it
            // to the readonly String
            answer += str[i];
        }
    }
    return answer;
}

// Driver code
public static void Main(String[] args)
{
    String str = "geeksforgeeks";
    Console.Write(longestVowelSubsequence(str)+"\n");
}
}

// This code is contributed by Princi Singh

Javascript

<script>

// Javascript program to find the longest
// subsequence containing only vowels

// Function to check whether
// a character is vowel or not
function isVowel(x)
{
    x = (x.toLowerCase());

    // Returns true if x is vowel
    return (x == 'a' || x == 'e'
            || x == 'i' || x == 'o'
            || x == 'u');
}

// Function to find the longest subsequence
// which contain all vowels
function longestVowelSubsequence(str)
{
    var answer = "";

    // Length of the string
    var n = str.length;

    // Iterating through the string
    for (var i = 0; i < n; i++) {

        // Checking if the character is a
        // vowel or not
        if (isVowel(str[i])) {

            // If it is a vowel, then add it
            // to the final string
            answer += str[i];
        }
    }

    return answer;
}

// Driver code
var str = "geeksforgeeks";
document.write( longestVowelSubsequence(str));

// This code is contributed by importantly.
</script>

Output:

eeoee

Time Complexity: O(N)
Auxiliary Space: O(N), The extra space is used to store the result.