Nth Even length Palindrome
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; } |
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
<?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 ?> |
Javascript
<script> // Javascript program to find nth even length Palindrome // Function to find nth even length Palindrome function evenlength(n) { // string r to store resultant // palindrome. Initialize same as s let res = n; // In this loop string r stores // reverse of string s after the // string s in consecutive manner for (let j = n.length - 1; j >= 0; --j) res += n[j]; return res; } // Driver code let n = "10" ; // Function call document.write(evenlength(n)); //This code is contributed by avanitrachhadiya2155 </script> |
1001
Time Complexity: O(n)
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