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/C++

// A C++ program to generate palindromic numbers // less than n. #include <iostream> 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; } // Fruition to print decimal palindromic number void generatePaldindromes(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; generatePaldindromes(n); return 0; }

## Python

# 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 generatePaldindromes(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), i = i + 1 # Driver Program to test above function n = 104 generatePaldindromes(n) #This code is contributed by Afzal Ansari

Output:

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

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 store it.

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