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# Nth Even length Palindrome

• Difficulty Level : Medium
• Last Updated : 14 Jul, 2022

Given a number n as a 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 reverse of 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 the implementation of this approach.

## C++

 `// C++ program to find n=th even length string.` `#include ` `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` `int` `main()` `{` `    ``string n = ``"10"``;` `  `  `    ``// Function call` `    ``cout << evenlength(n);` `    ``return` `0;` `}`

## Java

 `// 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 code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``String n = ``"10"``;` `      `  `        ``// Function call` `        ``System.out.println(evenlength(n));` `    ``}` `}`   `// Contributed by Pramod Kumar`

## Python3

 `# 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"`   `# Function call` `print``(evenlength(n))`   `# This code is contributed by` `# Mohit kumar 29`

## C#

 `// 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 code` `    ``public` `static` `void` `Main()` `    ``{` `        ``string` `n = ``"10"``;`   `        ``// Function call` `        ``Console.WriteLine(evenlength(n));` `    ``}` `}`   `// This code is contributed by vt_m.`

## PHP

 `= 0; --``\$j``)` `        ``\$res` `= ``\$res` `. ``\$n``[``\$j``];`   `    ``return` `\$res``;` `}`   `// Driver code` `\$n` `= ``"10"``;`   `// Function call` `echo` `evenlength(``\$n``);`   `// This code is contributed by ita_c` `?>`

## Javascript

 ``

Output

`1001`

Time Complexity: O(n)
Auxiliary Space: O(n)

This article is contributed by Aarti_Rathi and Surya Priy. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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