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Make palindromic string non-palindromic by rearranging its letters

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  • Difficulty Level : Medium
  • Last Updated : 15 Sep, 2022
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Given string str containing lowercase alphabets (a – z). The task is to print the string after rearranging some characters such that the string becomes non-palindromic. If it’s impossible to make the string non-palindrome then print -1.

Examples: 

Input: str = “abba” 
Output: aabb

Input: str = “zzz” 
Output: -1 

Approach: 

If all the characters in the string are the same then no matter how you rearrange the characters, the string will remain the same and will be palindromic. Now, if a non-palindromic arrangement exists, the best way to rearrange the characters is to sort the string which will form a continuous segment of the same characters and will never be palindromic. In order to reduce the time required to sort the string, we can store the frequencies of all 26 characters and print them in a sorted manner.

Below is the implementation of the above approach: 

C++




// CPP Program to rearrange letters of string
// to find a non-palindromic string if it exists
#include <bits/stdc++.h>
using namespace std;
 
// Function to print the non-palindromic string
// if it exists, otherwise prints -1
void findNonPalinString(string s)
{
    int freq[26] = { 0 }, flag = 0;
 
    for (int i = 0; i < s.size(); i++) {
 
        // If all characters are not
        // same, set flag to 1
        if (s[i] != s[0])
            flag = 1;
 
        // Update frequency of the current character
        freq[s[i] - 'a']++;
    }
 
    // If all characters are same
    if (!flag)
        cout << "-1";
    else {
 
        // Print characters in sorted manner
        for (int i = 0; i < 26; i++)
            for (int j = 0; j < freq[i]; j++)
                cout << char('a' + i);
    }
}
 
// Driver Code
int main()
{
    string s = "abba";
 
    findNonPalinString(s);
 
    return 0;
}

Java




// Java Program to rearrange letters of string
// to find a non-palindromic string if it exists
class GfG
{
 
// Function to print the non-palindromic string
// if it exists, otherwise prints -1
static void findNonPalinString(char s[])
{
    int freq[] = new int[26];
    int flag = 0;
 
    for (int i = 0; i < s.length; i++)
    {
 
        // If all characters are not
        // same, set flag to 1
        if (s[i] != s[0])
            flag = 1;
 
        // Update frequency of
        // the current character
        freq[s[i] - 'a']++;
    }
 
    // If all characters are same
    if (flag == 0)
        System.out.println("-1");
    else
    {
 
        // Print characters in sorted manner
        for (int i = 0; i < 26; i++)
            for (int j = 0; j < freq[i]; j++)
                System.out.print((char)('a' + i));
    }
}
 
// Driver Code
public static void main(String[] args)
{
    String s = "abba";
     
    findNonPalinString(s.toCharArray());
}
}
 
// This code is contributed by
// Prerna Saini.

Python3




# Python3 Program to rearrange letters of string
# to find a non-palindromic string if it exists
 
# Function to print the non-palindromic string
# if it exists, otherwise prints -1
def findNonPalinString(s):
 
    freq = [0] * (26)
    flag = 0
 
    for i in range(0, len(s)):
 
        # If all characters are not same,
        # set flag to 1
        if s[i] != s[0]:
            flag = 1
 
        # Update frequency of the current
        # character
        freq[ord(s[i]) - ord('a')] += 1
 
    # If all characters are same
    if not flag:
        print("-1")
     
    else:
         
        # Print characters in sorted manner
        for i in range(0, 26):
            for j in range(0, freq[i]):
                print(chr(ord('a') + i),
                               end = "")
 
# Driver Code
if __name__ == "__main__":
 
    s = "abba"
    findNonPalinString(s)
 
# This code is contributed by
# Rituraj Jain

C#




// C# Program to rearrange letters
// of string to find a non-palindromic
// string if it exists
using System;
 
class GfG
{
 
    // Function to print the
    // non-palindromic string
    // if it exists, otherwise
    // prints -1
    static void findNonPalinString(char []s)
    {
        int []freq = new int[26];
        int flag = 0;
     
        for (int i = 0; i < s.Length; i++)
        {
     
            // If all characters are not
            // same, set flag to 1
            if (s[i] != s[0])
                flag = 1;
     
            // Update frequency of
            // the current character
            freq[s[i] - 'a']++;
        }
     
        // If all characters are same
        if (flag == 0)
            Console.WriteLine("-1");
        else
        {
     
            // Print characters in sorted manner
            for (int i = 0; i < 26; i++)
                for (int j = 0; j < freq[i]; j++)
                        Console.Write((char)('a' + i));
        }
    }
     
    // Driver Code
    public static void Main()
    {
        string s = "abba";
         
        findNonPalinString(s.ToCharArray());
    }
}
 
// This code is contributed by Ryuga

Javascript




<script>
 
// JavaScript Program to rearrange letters of string
// to find a non-palindromic string if it exists
 
// Function to print the non-palindromic string
// if it exists, otherwise prints -1
function findNonPalinString(s)
{
    var freq = Array.from({length: 26}, (_, i) => 0);
    var flag = 0;
 
    for (var i = 0; i < s.length; i++)
    {
 
        // If all characters are not
        // same, set flag to 1
        if (s[i] != s[0])
            flag = 1;
 
        // Update frequency of
        // the current character
        freq[s[i].charCodeAt(0) -
        'a'.charCodeAt(0)]++;
    }
 
    // If all characters are same
    if (flag == 0)
        document.write("-1");
    else
    {
 
        // Print characters in sorted manner
        for (var i = 0; i < 26; i++)
            for (var j = 0; j < freq[i]; j++)
                document.write(String.fromCharCode
                ('a'.charCodeAt(0) + i));
    }
}
 
// Driver Code
var s = "abba";
 
findNonPalinString(s.split(''));
 
// This code contributed by shikhasingrajput
 
</script>

Output

aabb

Complexity Analysis:

  • Time Complexity: O(N)
  • Auxiliary Space: O(1)

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