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 <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` `int` `main()` `{` ` ` `string n = ` `"10"` `;` ` ` ` ` `// Function call` ` ` `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 code` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `String n = ` `"10"` `;` ` ` ` ` `// Function call` ` ` `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"` `# Function call` `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 code` ` ` `public` `static` `void` `Main()` ` ` `{` ` ` `string` `n = ` `"10"` `;` ` ` `// Function call` ` ` `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` `$n` `= ` `"10"` `;` `// Function call` `echo` `evenlength(` `$n` `);` `// This code is contributed by ita_c` `?>` |

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**Output**

1001

**Time Complexity: **O(n)

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