Check if characters of a given string can be rearranged to form a palindrome

Given a string, Check if characters of the given string can be rearranged to form a palindrome.
For example characters of “geeksogeeks” can be rearranged to form a palindrome “geeksoskeeg”, but characters of “geeksforgeeks” cannot be rearranged to form a palindrome.

A set of characters can form a palindrome if at most one character occurs odd number of times and all characters occur even number of times.

A simple solution is to run two loops, the outer loop picks all characters one by one, the inner loop counts number of occurrences of the picked character. We keep track of odd counts. Time complexity of this solution is O(n²).

We can do it in O(n) time using a count array. Following are detailed steps.
1) Create a count array of alphabet size which is typically 256. Initialize all values of count array as 0.
2) Traverse the given string and increment count of every character.
3) Traverse the count array and if the count array has more than one odd values, return false. Otherwise return true.

Below is the implementation of above approach.

C++

// C++ implementation to check if 
// characters of a given string can 
// be rearranged to form a palindrome 
#include<bits/stdc++.h> 
using namespace std; 
#define NO_OF_CHARS 256 
   
/* function to check whether characters of a string can form  
   a palindrome */
bool canFormPalindrome(string str) 
{ 
    // Create a count array and initialize all  
    // values as 0 
    int count[NO_OF_CHARS] = {0}; 
   
    // For each character in input strings, 
    // increment count in the corresponding 
    // count array 
    for (int i = 0; str[i];  i++) 
        count[str[i]]++; 
   
    // Count odd occurring characters 
    int odd = 0; 
    for (int i = 0; i < NO_OF_CHARS; i++) 
    { 
        if (count[i] & 1) 
            odd++; 
  
        if (odd > 1) 
            return false; 
    } 
   
    // Return true if odd count is 0 or 1,  
    return true; 
} 
   
/* Driver program*/
int main() 
{ 
  canFormPalindrome("geeksforgeeks")? cout << "Yes
":  
                                     cout << "No
"; 
  canFormPalindrome("geeksogeeks")? cout << "Yes
":  
                                    cout << "No
"; 
  return 0; 
} 

Java

// Java implementation to check if 
// characters of a given string can 
// be rearranged to form a palindrome 
import java.io.*; 
import java.util.*; 
import java.math.*; 
  
class GFG { 
  
static int NO_OF_CHARS = 256; 
  
    /* function to check whether characters  
    of a string can form a palindrome */
    static boolean canFormPalindrome(String str) { 
      
    // Create a count array and initialize all 
    // values as 0 
    int count[] = new int[NO_OF_CHARS]; 
    Arrays.fill(count, 0); 
  
    // For each character in input strings, 
    // increment count in the corresponding 
    // count array 
    for (int i = 0; i < str.length(); i++) 
    count[(int)(str.charAt(i))]++; 
  
    // Count odd occurring characters 
    int odd = 0; 
    for (int i = 0; i < NO_OF_CHARS; i++)  
    { 
    if ((count[i] & 1) == 1) 
        odd++; 
  
    if (odd > 1) 
        return false; 
    } 
  
    // Return true if odd count is 0 or 1, 
    return true; 
} 
  
// Driver program 
public static void main(String args[]) 
{ 
    if (canFormPalindrome("geeksforgeeks")) 
    System.out.println("Yes"); 
    else
    System.out.println("No"); 
  
    if (canFormPalindrome("geeksogeeks")) 
    System.out.println("Yes"); 
    else
    System.out.println("No"); 
} 
} 
  
// This code is contributed by Nikita Tiwari. 

C#

// C# implementation to check if 
// characters of a given string can 
// be rearranged to form a palindrome 
  
using System; 
   
class GFG { 
   
static int NO_OF_CHARS = 256; 
   
    /* function to check whether characters  
    of a string can form a palindrome */
    static bool canFormPalindrome(string str) { 
       
    // Create a count array and initialize all 
    // values as 0 
    int[] count = new int[NO_OF_CHARS]; 
    Array.Fill(count, 0); 
   
    // For each character in input strings, 
    // increment count in the corresponding 
    // count array 
    for (int i = 0; i < str.Length; i++) 
    count[(int)(str[i])]++; 
   
    // Count odd occurring characters 
    int odd = 0; 
    for (int i = 0; i < NO_OF_CHARS; i++)  
    { 
    if ((count[i] & 1) == 1) 
        odd++; 
   
    if (odd > 1) 
        return false; 
    } 
   
    // Return true if odd count is 0 or 1, 
    return true; 
} 
   
// Driver program 
public static void Main() 
{ 
    if (canFormPalindrome("geeksforgeeks")) 
    Console.WriteLine("Yes"); 
    else
    Console.WriteLine("No"); 
   
    if (canFormPalindrome("geeksogeeks")) 
    Console.WriteLine("Yes"); 
    else
    Console.WriteLine("No"); 
} 
} 
  

Python3

# Python3 implementation to check if 
# characters of a given string can 
# be rearranged to form a palindrome 
  
NO_OF_CHARS = 256
  
# function to check whether characters 
# of a string can form a palindrome  
def canFormPalindrome(st) : 
  
    # Create a count array and initialize   
    # all values as 0 
    count = [0] * (NO_OF_CHARS) 
  
    # For each character in input strings, 
    # increment count in the corresponding 
    # count array 
    for i in range( 0, len(st)) : 
        count[ord(st[i])] = count[ord(st[i])] + 1
  
    # Count odd occurring characters 
    odd = 0
      
    for i in range(0, NO_OF_CHARS ) : 
        if (count[i] & 1) : 
            odd = odd + 1
  
        if (odd > 1) : 
            return False
              
    # Return true if odd count is 0 or 1,  
    return True
  
# Driver program 
if(canFormPalindrome("geeksforgeeks")) : 
    print("Yes") 
else : 
    print("No") 
      
if(canFormPalindrome("geeksogeeks")) : 
    print("Yes") 
else : 
    print("No") 
  
# This code is contributed by Nikita Tiwari. 

Output:

No
Yes

Check if characters of a given string can be rearranged to form a palindrome

C++

Java

C#

Python3

tags:

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