通过重新排列字母来使回文字符串变为非回文字符串

给定一个包含小写字母(a – z)的字符串str 。任务是在重新排列某些字符后打印该字符串，以使该字符串变为非回文。如果不可能使字符串非回文，则打印-1 。

例子：

Input: str = “abba”
Output: aabb

Input: str = “zzz”
Output: -1

方法：如果字符串中的所有字符都相同，那么无论您如何重新排列字符，字符串都将保持不变并且回文。现在，如果存在非回文排列，则重新排列字符的最佳方法是对字符串进行排序，该字符串将形成相同字符的连续段，并且永远不会回文。为了减少对字符串进行排序所需的时间，我们可以存储所有26个字符的频率并以排序方式打印它们。

下面是上述方法的实现：

C++

// CPP Program to rearrange letters of string
// to find a non-palindromic string if it exists
#include 
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

输出：

aabb