Nth Even length Palindrome

Given a number n as string, find the nth even-length positive palindrome number .

Examples:

Input : n = "1"
Output : 11
1st even-length palindrome is 11 .

Input : n = "10"
Output : 1001
The first 10 even-length palindrome numbers are 11, 22, 
33, 44, 55, 66, 77, 88, 99 and 1001.



As, it is a even-length palindrome so its first half should be equal to second half and length will be 2, 4, 6, 8 …. To evaluate nth palindrome let’s just see 1st 10 even-length palindrome numbers 11, 22, 33, 44, 55, 66, 77, 88, 99 and 1001 . Here, nth palindrome is nn’ where n’ is reverse of n . Thus we just have to write n and n’ in a consecutive manner where n’ is reverse of n .

Below is implementation of this approach .

C/C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to find n=th even length string.
#include <bits/stdc++.h>
using namespace std;
  
// Function to find nth even length Palindrome
string evenlength(string n)
{
    // string r to store resultant
    // palindrome. Initialize same as s
    string res = n;
  
    // In this loop string r stores
    // reverse of string s after the
    // string s in consecutive manner .
    for (int j = n.length() - 1; j >= 0; --j)
        res += n[j];
  
    return res;
}
  
// Driver code to test above function
int main()
{
    string n = "10";
    cout << evenlength(n);
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to find nth even length Palindrome
import java.io.*;
  
class GFG {
    // Function to find nth even length Palindrome
    static String evenlength(String n)
    {
        // string r to store resultant
        // palindrome. Initialize same as s
        String res = n;
  
        // In this loop string r stores
        // reverse of string s after the
        // string s in consecutive manner
        for (int j = n.length() - 1; j >= 0; --j)
            res += n.charAt(j);
  
        return res;
    }
  
    // driver program
    public static void main(String[] args)
    {
        String n = "10";
        System.out.println(evenlength(n));
    }
}
  
// Contributed by Pramod Kumar

chevron_right


Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 program to find n=th even 
# length string.
import math as mt
  
# Function to find nth even length 
# Palindrome
def evenlength(n):
  
    # string r to store resultant
    # palindrome. Initialize same as s
    res = n
  
    # In this loop string r stores
    # reverse of string s after the
    # string s in consecutive manner .
    for j in range(len(n) - 1, -1, -1):
        res += n[j]
  
    return res
  
# Driver code
n = "10"
print(evenlength(n))
  
# This code is contributed by
# Mohit kumar 29

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program to find nth even
// length Palindrome
using System;
  
class GFG {
      
    // Function to find nth even
    // length Palindrome
    static string evenlength(string n)
    {
          
        // string r to store resultant
        // palindrome. Initialize same
        // as s
        string res = n;
  
        // In this loop string r stores
        // reverse of string s after
        // the string s in consecutive
        // manner
        for (int j = n.Length - 1;
                           j >= 0; --j)
            res += n[j];
  
        return res;
    }
  
    // driver program
    public static void Main()
    {
        string n = "10";
          
        Console.WriteLine(evenlength(n));
    }
}
  
// This code is contributed by vt_m.

chevron_right


PHP

filter_none

edit
close

play_arrow

link
brightness_4
code

<?php
// PHP program to find n=th even length string.
  
// Function to find nth even length Palindrome
function evenlength($n)
{
    // string r to store resultant
    // palindrome. Initialize same as s
    $res = $n;
  
    // In this loop string r stores
    // reverse of string s after the
    // string s in consecutive manner .
    for ($j = strlen($n) - 1; $j >= 0; --$j)
        $res = $res . $n[$j];
  
    return $res;
}
  
// Driver code
$n = "10";
echo evenlength($n);
  
// This code is contributed by ita_c
?>

chevron_right



Output:

 1001

Time Complexity : O(n)
This article is contributed by Surya Priy. 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.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



My Personal Notes arrow_drop_up

Improved By : vt_m, Ita_c, mohit kumar 29



Article Tags :
Practice Tags :


Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.