Check if binary representation of a number is palindrome or not

Check if the binary representation of a positive number is palindrome or not.

For example, 101, 11, 11011, 1001001 are palindromes. 100, 110, 1011, etc., are not palindromes.

Practice this problem

The idea is simple – construct a reverse of the binary representation of n and return true if it is the same as n. The implementation can be seen below in C++, Java, and Python:

C++

#include <iostream>

using namespace std;

// Returns true if the binary representation of `n` is a palindrome

bool isPalindrome(unsigned n)

{

// `rev` stores reverse of a binary representation of `n`

unsigned rev = 0;

// do till all bits of `n` are processed

unsigned k = n;

while (k)

{

// add the rightmost bit to `rev`

rev = (rev << 1) | (k & 1);

k = k >> 1; // drop last bit

}

// Returns true if `reverse(n)` is the same as `n`

return n == rev;

}

int main()

{

int n = 9; // 1001

if (isPalindrome(n)) {

cout << n << " is a palindrome";

}

else {

cout << n << " is not a palindrome";

}

return 0;

}

Download Run Code

Output:

9 is a palindrome

Java

class Main

{

// Returns true if the binary representation of `n` is a palindrome

public static boolean isPalindrome(int n)

{

// `rev` stores reverse of a binary representation of `n`

int rev = 0;

// do till all bits of `n` are processed

int k = n;

while (k > 0)

{

// add the rightmost bit to `rev`

rev = (rev << 1) | (k & 1);

k = k >> 1; // drop last bit

}

// Returns true if `reverse(n)` is the same as `n`

return n == rev;

}

public static void main(String[] args)

{

int n = 9; // 1001

if (isPalindrome(n)) {

System.out.println(n + " is a palindrome");

}

else {

System.out.println(n + " is not a palindrome");

}

Download Run Code

Output:

9 is a palindrome

Python

# Returns true if the binary representation of `n` is a palindrome

def isPalindrome(n):

# `rev` stores reverse of a binary representation of `n`

rev = 0

# do till all bits of `n` are processed

k = n

while k > 0:

# add the rightmost bit to `rev`

rev = (rev << 1) | (k & 1)

k = k >> 1 # drop last bit

# Returns true if `reverse(n)` is the same as `n`

return n == rev

if __name__ == '__main__':

n = 9 # 1001

if isPalindrome(n):

print(f'{n} is a palindrome')

else:

print(f'{n} is not a palindrome')

Download Run Code

Output:

9 is a palindrome

Also See:

Bit Hacks – Part 1 (Basic)
Bit Hacks – Part 2 (Playing with k’th bit)
Bit Hacks – Part 3 (Playing with the rightmost set bit of a number)
Bit Hacks – Part 4 (Playing with letters of the English alphabet)
Bit Hacks – Part 5 (Find the absolute value of an integer without branching)