# 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
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++

 `// C++ implementation of lexicographically first ` `// alternate vowel and consonant string ` `#include ` `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; ` `} `

## Java

 `// 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 `

## Python3

 `# Python3 implementation of lexicographically first ` `# alternate vowel and consonant string ` `SIZE ``=` `26` ` `  `# 'ch' is vowel or not ` `def` `isVowel(ch): ` `    ``if` `(ch ``=``=` `'a'` `or` `ch ``=``=` `'e'` `or`  `        ``ch ``=``=` `'i'` `or` `ch ``=``=` `'o'` `or`  `        ``ch ``=``=` `'u'``): ` `        ``return` `True` `    ``return` `False` ` `  `# create alternate vowel and consonant string ` `# str1[0...l1-1] and str2[start...l2-1] ` `def` `createAltStr(str1, str2, start, l): ` `    ``finalStr ``=` `"" ` `    ``i ``=` `0` `    ``j ``=` `start ` ` `  `    ``# first adding character of vowel/consonant ` `    ``# then adding character of consonant/vowel ` `    ``while` `j < l: ` `        ``finalStr ``+``=` `str1[i] ``+` `str2[j] ` `        ``i ``+``=` `1` `        ``j ``+``=` `1` `    ``return` `finalStr ` ` `  `# function to find the required lexicographically ` `# first alternate vowel and consonant string ` `def` `findAltStr(string): ` ` `  `    ``# hash table to store frequencies ` `    ``# of each character in 'str' ` `    ``char_freq ``=` `[``0``] ``*` `SIZE ``# initilaize all elements  ` `                           ``# of char_freq[] to 0 ` `    ``nv ``=` `0` `    ``nc ``=` `0` `    ``vstr ``=` `"" ` `    ``cstr ``=` `"" ` `    ``l ``=` `len``(string) ` ` `  `    ``for` `i ``in` `range``(l): ` `        ``ch ``=` `string[i] ` ` `  `        ``# count vowels ` `        ``if` `isVowel(ch): ` `            ``nv ``+``=` `1` ` `  `        ``# count consonants ` `        ``else``: ` `            ``nc ``+``=` `1` ` `  `        ``# update frequency of 'ch' in ` `        ``# char_freq[] ` `        ``char_freq[``ord``(ch) ``-` `97``] ``+``=` `1` ` `  `    ``# 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` `i ``in` `range``(SIZE): ` `        ``ch ``=` `chr``(i ``+` `97``) ` `        ``for` `j ``in` `range``(``1``, char_freq[i] ``+` `1``): ` `            ``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 ` `if` `__name__ ``=``=` `"__main__"``: ` `    ``string ``=` `"aeroplane"` `    ``print``(findAltStr(string)) ` ` `  `# This code is contributed by ` `# sanjeev2552 `

## C#

 `// 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 + 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 + createAltStr(vstr, ` `                    ``cstr, 1, nc)); ` `        ``} ` ` `  `        ``// if both vowel and consonant  ` `        ``// strings are of equal length  ` `        ``// start creating String with consonant  ` `        ``if` `(cstr < vstr)  ` `        ``{ ` `            ``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*/`

Output:

```alanepero
```

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

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