# 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++

`// 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; ` `} ` |

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## 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 ` |

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## 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 ` |

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## 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. ` |

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## PHP

`<?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 ` `?> ` |

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**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.

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