Sort an Array of Strings according to the number of Vowels in them

// Java implementation of the approach 
import java.util.*;
import java.lang.*;
import java.io.*;

class GFG{

static class pair
{
    int first;
    String second;
    
    pair(int first,String second)
    {
        this.first = first;
        this.second = second;
    }
}

// Function to check the Vowel
static boolean isVowel(char ch)
{
    ch = Character.toUpperCase(ch);
    return (ch == 'A' || ch == 'E' || 
            ch == 'I' || ch == 'O' ||
            ch == 'U');
}

// Returns count of vowels in str
static int countVowels(String str)
{
    int count = 0;
    for(int i = 0; i < str.length(); i++)
    
        // Check for vowel
        if (isVowel(str.charAt(i))) 
            ++count;
            
    return count;
}

// Function to sort the array according to
// the number of the vowels
static void sortArr(String arr[], int n)
{
    
    // Vector to store the number of vowels
    // with respective elements
    ArrayList<pair> vp = new ArrayList<>();

    // Inserting number of vowels
    // with respective strings
    // in the vector pair
    for(int i = 0; i < n; i++) 
    {
        vp.add(new pair(countVowels(arr[i]),
                                    arr[i]));
    }

    // Sort the vector, this will sort the pair
    // according to the number of vowels
    Collections.sort(vp, (a, b) -> a.first - b.first);
    
    // Print the sorted vector content
    for(int i = 0; i < vp.size(); i++)
        System.out.print(vp.get(i).second + " ");
}

// Driver code
public static void main(String[] args) 
{
    String arr[] = { "lmno", "pqrst",
                     "aeiou", "xyz" };
    int n = arr.length;
    
    sortArr(arr, n);
}
}

// This code is contributed by offbeat

import java.util.*;

public class GFG {
    // Function to count the number of vowels in a word
    public static int countVowels(String word)
    {
        // A string of all vowels
        String vowels = "aeiouAEIOU";
        int count = 0;
        for (int i = 0; i < word.length(); i++) {
            // If the character is a vowel, increment the
            // count
            if (vowels.indexOf(word.charAt(i)) != -1) {
                count++;
            }
        }
        return count;
    }

    // Function to sort a list of strings based on the
    // number of vowels in each string
    public static List<String>
    sortStrings(List<String> strings)
    {
        // Sort the list of strings based on the number of
        // vowels in each string
        Collections.sort(strings, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2)
            {
                return countVowels(s1) - countVowels(s2);
            }
        });
        return strings;
    }

    // Main function
    public static void main(String[] args)
    {
        // Input list of strings
        List<String> strings = Arrays.asList(
            "lmno", "pqrst", "aeiou", "xyz");
        // Sort the list of strings
        List<String> sortedStrings = sortStrings(strings);
        // Print the sorted list of strings
        System.out.println(sortedStrings);
    }
}