# 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.
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++

 `// 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 to test above function ` `int` `main() ` `{ ` `    ``string n = ``"10"``; ` `    ``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 program ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``String n = ``"10"``; ` `        ``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"` `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 program ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``string` `n = ``"10"``; ` `         `  `        ``Console.WriteLine(evenlength(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m. `

## PHP

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

Output:

``` 1001
```

Time Complexity : O(n)
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