Lexicographically first alternate vowel and consonant string

Given a string str. The problem is to rearrange characters of the given string such that the vowels and consonants occupy alternate position and the string so formed should be lexicographically (alphabetically) smallest. If string can not be rearranged in desired way, print “no such string”.

Examples:

Input : mango
Output : gamon
It could be arranged in other ways too, like
manog, etc., but gamon is lexicographically
smallest.

Input : aeroplane
Output : alanepero



Approach: Following are the steps:

  1. Store frequency of each character of input string in a hash table.
  2. Count number of vowels and consonants in given string.
  3. If difference between counts is more than one, return “Not Possible”.
  4. Else, form separate vowel and consonant strings with the help of the hash table having frequencies of each character of the input string. Note, while creating vowel and consonant strings, the characters in respective strings should be in alphabetical order.
  5. If there are more vowels than consonants, print first vowel first and then print remaining characters from consonant and vowel strings alternately.
  6. If there are more consonants than vowels, print first consonat first and then print remaining characters from vowel and consonant strings alternately.
  7. If counts are same, compare first vowel with first consonant and print the smaller one first and then continue printing alternately.

C++

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// C++ implementation of lexicographically first
// alternate vowel and consonant string
#include <bits/stdc++.h>
using namespace std;
  
#define SIZE 26
  
// 'ch' is vowel or not
bool isVowel(char ch)
{
    if (ch == 'a' || ch == 'e' || ch == 'i' || 
                       ch == 'o' || ch == 'u')
        return true;
    return false;
}
  
// create alternate vowel and consonant string
// str1[0...l1-1] and str2[start...l2-1]
string createAltStr(string str1, string str2,
                    int start, int l)
{
    string finalStr = "";
  
    // first adding character of vowel/consonant
    // then adding character of consonant/vowel
    for (int i = 0, j = start; j < l; i++, j++)
        finalStr = (finalStr + str1.at(i)) +
                                 str2.at(j);
    return finalStr;
}
  
// function to find the required lexicographically
// first alternate vowel and consonant string
string findAltStr(string str)
{
    // hash table to store frequencies
    // of each character in 'str'
    int char_freq[SIZE];
  
    // initilaize all elements of char_freq[]
    // to 0
    memset(char_freq, 0, sizeof(char_freq));
  
    int nv = 0, nc = 0;
    string vstr = "", cstr = "";
    int l = str.size();
  
    for (int i = 0; i < l; i++) {
        char ch = str.at(i);
  
        // count vowels
        if (isVowel(ch))
            nv++;
  
        // count consonants
        else
            nc++;
  
        // update frequency of 'ch' in
        // char_freq[]
        char_freq[ch - 97]++;
    }
  
    // no such string can be formed
    if (abs(nv - nc) >= 2)
        return "no such string";
  
    // form the vowel string 'vstr' and
    // consonant string 'cstr' which contains
    // characters in lexicographical order
    for (int i = 0; i < SIZE; i++) {
        char ch = (char)(i + 97);
        for (int j = 1; j <= char_freq[i]; j++) {
            if (isVowel(ch))
                vstr += ch;
            else
                cstr += ch;
        }
    }
  
    // remove first character of vowel string
    // then create alternate string with
    // cstr[0...nc-1] and vstr[1...nv-1]
    if (nv > nc)
        return (vstr.at(0) + createAltStr(cstr,
                                 vstr, 1, nv));
  
    // remove first character of consonant string
    // then create alternate string with
    // vstr[0...nv-1] and cstr[1...nc-1]
    if (nc > nv)
        return (cstr.at(0) + createAltStr(vstr, 
                                  cstr, 1, nc));
  
    // if both vowel and consonant
    // strings are of equal length
    // start creating string with consonant
    if (cstr.at(0) < vstr.at(0))
        return createAltStr(cstr, vstr, 0, nv);
  
    // start creating string with vowel
    return createAltStr(vstr, cstr, 0, nc);
}
  
// Driver program to test above
int main()
{
    string str = "aeroplane";
    cout << findAltStr(str);
    return 0;
}

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Java

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// Java implementation of lexicographically first 
// alternate vowel and consonant String 
import java.util.Arrays;
class GFG {
  
    static final int SIZE = 26;
  
    // 'ch' is vowel or not 
    static boolean isVowel(char ch)
    {
        if (ch == 'a' || ch == 'e' || ch == 'i'
                || ch == 'o' || ch == 'u')
        {
            return true;
        }
        return false;
    }
  
    // create alternate vowel and consonant String 
    // str1[0...l1-1] and str2[start...l2-1] 
    static String createAltStr(String str1, String str2,
            int start, int l)
    {
        String finalStr = "";
  
        // first adding character of vowel/consonant 
        // then adding character of consonant/vowel 
        for (int i = 0, j = start; j < l; i++, j++) 
        {
            finalStr = (finalStr + str1.charAt(i))
                    + str2.charAt(j);
        }
        return finalStr;
    }
  
    // function to find the required 
    // lexicographically  first alternate 
    // vowel and consonant String 
    static String findAltStr(String str)
    {
          
        // hash table to store frequencies 
        // of each character in 'str' 
        int char_freq[] = new int[SIZE];
  
        // initilaize all elements of char_freq[] 
        // to 0 
        Arrays.fill(char_freq, 0);
  
        int nv = 0, nc = 0;
        String vstr = "", cstr = "";
        int l = str.length();
  
        for (int i = 0; i < l; i++)
        {
            char ch = str.charAt(i);
  
            // count vowels 
            if (isVowel(ch)) 
            {
                nv++;
            
              
            // count consonants 
            else 
            {
                nc++;
            }
  
            // update frequency of 'ch' in 
            // char_freq[] 
            char_freq[ch - 97]++;
        }
  
        // no such String can be formed 
        if (Math.abs(nv - nc) >= 2)
        {
            return "no such String";
        }
  
        // form the vowel String 'vstr' and 
        // consonant String 'cstr' which contains 
        // characters in lexicographical order 
        for (int i = 0; i < SIZE; i++) {
            char ch = (char) (i + 97);
            for (int j = 1; j <= char_freq[i]; j++) 
            {
                if (isVowel(ch)) 
                {
                    vstr += ch;
                
                else
                {
                    cstr += ch;
                }
            }
        }
  
        // remove first character of vowel String 
        // then create alternate String with 
        // cstr[0...nc-1] and vstr[1...nv-1] 
        if (nv > nc) {
            return (vstr.charAt(0) + createAltStr(cstr,
                    vstr, 1, nv));
        }
  
        // remove first character of consonant String 
        // then create alternate String with 
        // vstr[0...nv-1] and cstr[1...nc-1] 
        if (nc > nv) 
        {
            return (cstr.charAt(0) + createAltStr(vstr,
                    cstr, 1, nc));
        }
  
        // if both vowel and consonant 
        // strings are of equal length 
        // start creating String with consonant 
        if (cstr.charAt(0) < vstr.charAt(0)) 
        {
            return createAltStr(cstr, vstr, 0, nv);
        }
  
        // start creating String with vowel 
        return createAltStr(vstr, cstr, 0, nc);
    }
  
    // Driver code 
    public static void main(String[] args) {
        String str = "aeroplane";
        System.out.println(findAltStr(str));
    }
  
// This code is contributed by 29AjayKumar

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C#

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// C# implementation of lexicographically first 
// alternate vowel and consonant String 
using System;
  
class GFG 
{
    static readonly int SIZE = 26;
  
    // 'ch' is vowel or not 
    static bool isVowel(char ch)
    {
        if (ch == 'a' || ch == 'e' || ch == 'i'
                || ch == 'o' || ch == 'u')
        {
            return true;
        }
        return false;
    }
  
    // create alternate vowel and consonant String 
    // str1[0...l1-1] and str2[start...l2-1] 
    static String createAltStr(String str1, String str2,
            int start, int l)
    {
        String finalStr = "";
  
        // first adding character of vowel/consonant 
        // then adding character of consonant/vowel 
        for (int i = 0, j = start; j < l; i++, j++) 
        {
            finalStr = (finalStr + str1[i]) + 
                                    str2[j];
        }
        return finalStr;
    }
  
    // function to find the required 
    // lexicographically first alternate 
    // vowel and consonant String 
    static String findAltStr(String str)
    {
          
        // hash table to store frequencies 
        // of each character in 'str' 
        int []char_freq = new int[SIZE];
  
        int nv = 0, nc = 0;
        String vstr = "", cstr = "";
        int l = str.Length;
  
        for (int i = 0; i < l; i++)
        {
            char ch = str[i];
  
            // count vowels 
            if (isVowel(ch)) 
            {
                nv++;
            
              
            // count consonants 
            else
            {
                nc++;
            }
  
            // update frequency of 'ch' in 
            // char_freq[] 
            char_freq[ch - 97]++;
        }
  
        // no such String can be formed 
        if (Math.Abs(nv - nc) >= 2)
        {
            return "no such String";
        }
  
        // form the vowel String 'vstr' and 
        // consonant String 'cstr' which contains 
        // characters in lexicographical order 
        for (int i = 0; i < SIZE; i++) 
        {
            char ch = (char) (i + 97);
            for (int j = 1; j <= char_freq[i]; j++) 
            {
                if (isVowel(ch)) 
                {
                    vstr += ch;
                
                else
                {
                    cstr += ch;
                }
            }
        }
  
        // remove first character of vowel String 
        // then create alternate String with 
        // cstr[0...nc-1] and vstr[1...nv-1] 
        if (nv > nc) 
        {
            return (vstr[0] + createAltStr(cstr,
                    vstr, 1, nv));
        }
  
        // remove first character of consonant String 
        // then create alternate String with 
        // vstr[0...nv-1] and cstr[1...nc-1] 
        if (nc > nv) 
        {
            return (cstr[0] + createAltStr(vstr,
                    cstr, 1, nc));
        }
  
        // if both vowel and consonant 
        // strings are of equal length 
        // start creating String with consonant 
        if (cstr[0] < vstr[0]) 
        {
            return createAltStr(cstr, vstr, 0, nv);
        }
  
        // start creating String with vowel 
        return createAltStr(vstr, cstr, 0, nc);
    }
  
    // Driver code 
    public static void Main(String[] args) 
    {
        String str = "aeroplane";
        Console.WriteLine(findAltStr(str));
    }
}
  
/* This code has been contributed
by PrinciRaj1992*/

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Output:

alanepero

Time Complexity: O(n), where n is the length of the string.

This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Improved By : 29AjayKumar, princiraj1992