# Generate all palindromic numbers less than n

• Difficulty Level : Medium
• Last Updated : 24 Jan, 2022

Find all numbers less than n, which are palindromic. Numbers can be printed in any order.

Examples :

```Input : n = 12
Output : 1, 2, 3, 4, 5, 6, 7, 8, 9, 11

Input : n = 104
Output : 1, 2, 3, 4, 5, 6, 7, 8, 9, 11,
22, 33, 44, 55, 66, 77, 88, 99, 101
[Note that below program prints these numbers
in different order]
```

Brute Force: We check all the numbers from 1 to n whether its decimal representation is palindrome or not.

Efficient Approach: We start from 1 and create palindromes of odd digit and even digits up to n. For every number (starting from 1), we append its reverse at end if we need even length palindrome numbers. For odd length palindrome, we append reverse of all digits except last one.

## C++

 `// A C++ program to generate palindromic numbers``// less than n.``#include ``using` `namespace` `std;` `// A utility for creating palindrome``int` `createPalindrome(``int` `input, ``int` `b, ``bool` `isOdd)``{``    ``int` `n = input;``    ``int` `palin = input;` `    ``// checks if number of digits is odd or even``    ``// if odd then neglect the last digit of input in``    ``// finding reverse as in case of odd number of``    ``// digits middle element occur once``    ``if` `(isOdd)``        ``n /= b;` `    ``// Creates palindrome by just appending reverse``    ``// of number to itself``    ``while` `(n > 0)``    ``{``        ``palin = palin * b + (n % b);``        ``n /= b;``    ``}``    ``return` `palin;``}` `// Function to print decimal palindromic number``void` `generatePalindromes(``int` `n)``{``    ``int` `number;` `    ``// Run two times for odd and even length palindromes``    ``for` `(``int` `j = 0; j < 2; j++)``    ``{``        ``// Creates palindrome numbers with first half as i.``        ``// Value of j decided whether we need an odd length``        ``// of even length palindrome.``        ``int` `i = 1;``        ``while` `((number = createPalindrome(i, 10, j % 2)) < n)``        ``{``            ``cout << number << ``" "``;``            ``i++;``        ``}``    ``}``}` `// Driver Program to test above function``int` `main()``{``    ``int` `n = 104;``    ``generatePalindromes(n);``    ``return` `0;``}`

## Java

 `// A Java program to generate palindromic``// numbers less than n.``class` `GFG {` `// A utility for creating palindrome``static` `int` `createPalindrome(``int` `input, ``int` `b, ``int` `isOdd) {``    ``int` `n = input;``    ``int` `palin = input;` `    ``// checks if number of digits is odd or even``    ``// if odd then neglect the last digit of input in``    ``// finding reverse as in case of odd number of``    ``// digits middle element occur once``    ``if` `(isOdd == ``1``)``        ``n /= b;` `    ``// Creates palindrome by just appending reverse``    ``// of number to itself``    ``while` `(n > ``0``) {``        ``palin = palin * b + (n % b);``        ``n /= b;``    ``}``    ``return` `palin;``}` `// Function to print decimal``// palindromic number``static` `void` `generatePalindromes(``int` `n) {``    ``int` `number;` `    ``// Run two times for odd and even``    ``// length palindromes``    ``for` `(``int` `j = ``0``; j < ``2``; j++) {` `    ``// Creates palindrome numbers with first``    ``// half as i. Value of j decided whether``    ``// we need an odd length of even length``    ``// palindrome.``        ``int` `i = ``1``;``        ``while` `((number = createPalindrome(i, ``10``, j % ``2``)) < n) {``            ``System.out.print(number + ``" "``);``            ``i++;``    ``}``    ``}``}` `// Driver code``public` `static` `void` `main(String[] args) {``    ``int` `n = ``104``;``    ``generatePalindromes(n);``}``}``// This code is contributed by Anant Agarwal.`

## Python3

 `# Generate all palindromic numbers less than n``# A Python program to generate palindromic numbers``# less than n.``def` `createPalindrome(inp, b, isOdd):``    ``n ``=` `inp``    ``palin ``=` `inp`` ` `    ``# checks if number of digits is odd or even``    ``# if odd then neglect the last digit of input in``    ``# finding reverse as in case of odd number of``    ``# digits middle element occur once``    ``if` `(isOdd):``        ``n ``=` `n ``/``/` `b`` ` `    ``# Creates palindrome by just appending reverse``    ``# of number to itself``    ``while` `(n > ``0``):``        ``palin ``=` `palin ``*` `b ``+` `(n ``%` `b)``        ``n ``=` `n ``/``/` `b``    ``return` `palin`` ` `# Function to print decimal palindromic number``def` `generatePalindromes(n):`` ` `    ``# Run two times for odd and even length palindromes``    ``for` `j ``in` `range``(``2``):``        ``# Creates palindrome numbers with first half as i.``        ``# Value of j decided whether we need an odd length``        ``# of even length palindrome.``        ``i ``=` `1``        ``while` `(createPalindrome(i, ``10``, j ``%` `2``) < n):``            ``print` `(createPalindrome(i, ``10``, j ``%` `2``),end``=``" "``)``            ``i ``=` `i ``+` `1`` ` `# Driver Program to test above function``n ``=` `104``generatePalindromes(n)` `#This code is contributed by Afzal Ansari`

## C#

 `// A C# program to generate palindromic``// numbers less than n.``using` `System;` `class` `GFG {` `// A utility for creating palindrome``static` `int` `createPalindrome(``int` `input, ``int` `b,``                            ``int` `isOdd)``{``    ``int` `n = input;``    ``int` `palin = input;` `    ``// checks if number of digits is odd``    ``// or even if odd then neglect the``    ``// last digit of input in finding reverse``    ``// as in case of odd number of digits``    ``// middle element occur once``    ``if` `(isOdd == 1)``        ``n /= b;` `    ``// Creates palindrome by just appending``    ``// reverse of number to itself``    ``while` `(n > 0)``    ``{``        ``palin = palin * b + (n % b);``        ``n /= b;``    ``}``    ``return` `palin;``}` `// Function to print decimal``// palindromic number``static` `void` `generatePalindromes(``int` `n)``{``    ``int` `number;` `    ``// Run two times for odd and even``    ``// length palindromes``    ``for` `(``int` `j = 0; j < 2; j++)``    ``{` `        ``// Creates palindrome numbers with first``        ``// half as i. Value of j decided whether``        ``// we need an odd length of even length``        ``// palindrome.``        ``int` `i = 1;``        ``while` `((number = createPalindrome(i, 10,``                                    ``j % 2)) < n)``        ``{``            ``Console.Write(number + ``" "``);``            ``i++;``    ``}``    ``}``}` `// Driver Code``public` `static` `void` `Main()``{``    ``int` `n = 104;``    ``generatePalindromes(n);``}``}` `// This code is contributed by Nitin Mittal.`

## PHP

 ` 0)``    ``{``        ``\$palin` `= ``\$palin` `* ``\$b` `+ ``intval``(``\$n` `% ``\$b``);``        ``\$n` `= ``intval``(``\$n` `/ ``\$b``);``    ``}``    ``return` `\$palin``;``}` `// Function to print decimal``// palindromic number``function` `generatePalindromes(``\$n``)``{``    ``\$number` `= 0;` `    ``// Run two times for odd and``    ``// even length palindromes``    ``for` `(``\$j` `= 0; ``\$j` `< 2; ``\$j``++)``    ``{``        ``// Creates palindrome numbers``        ``// with first half as i. Value``        ``// of j decided whether we need``        ``// an odd length of even length``        ``// palindrome.``        ``\$i` `= 1;``        ``while` `((``\$number` `=``                   ``createPalindrome(``\$i``, 10,``                                    ``\$j` `% 2)) < ``\$n``)``        ``{``            ``echo` `\$number` `. ``" "``;``            ``\$i``++;``        ``}``    ``}``}` `// Driver Code``\$n` `= 104;``generatePalindromes(``\$n``);``    ` `// This code is contributed by Sam007``?>`

## Javascript

 ``

Output :

`11 22 33 44 55 66 77 88 99 1 2 3 4 5 6 7 8 9 101 `

Note that the above program doesn’t print output in sorted order. To print in sorted order, we can store palindromes in a vector and sort it, and don’t forget to use the required header file.

This article is contributed by Shivam Pradhan (anuj_charm). 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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