Given an integer ‘x’, write a C function that returns true if binary representation of x is palindrome else return false.
For example a numbers with binary representation as 10..01 is palindrome and number with binary representation as 10..00 is not palindrome.
The idea is similar to checking a string is palindrome or not. We start from leftmost and rightmost bits and compare bits one by one. If we find a mismatch, then return false.
Algorithm:
isPalindrome(x)
1) Find number of bits in x using sizeof() operator.
2) Initialize left and right positions as 1 and n respectively.
3) Do following while left ‘l’ is smaller than right ‘r’.
..…..a) If bit at position ‘l’ is not same as bit at position ‘r’, then return false.
..…..b) Increment ‘l’ and decrement ‘r’, i.e., do l++ and r–-.
4) If we reach here, it means we didn’t find a mismatching bit.
To find the bit at a given position, we can use the idea similar to this post. The expression “x & (1 << (k-1))” gives us non-zero value if bit at k’th position from right is set and gives a zero value if if k’th bit is not set.
Following is the implementation of the above algorithm.
C/C++
// C++ Program to Check if binary representation // of a number is palindrome #include<iostream> using namespace std; // This function returns true if k'th bit in x // is set (or 1). For example if x (0010) is 2 // and k is 2, then it returns true bool isKthBitSet(unsigned int x, unsigned int k) { return (x & (1 << (k - 1))) ? true : false; } // This function returns true if binary // representation of x is palindrome. // For example (1000...001) is paldindrome bool isPalindrome(unsigned int x) { int l = 1; // Initialize left position int r = sizeof(unsigned int) * 8; // initialize right position // One by one compare bits while (l < r) { if (isKthBitSet(x, l) != isKthBitSet(x, r)) return false; l++; r--; } return true; } // Driver Code int main() { unsigned int x = 1 << 15 + 1 << 16; cout << isPalindrome(x) << endl; x = 1 << 31 + 1; cout << isPalindrome(x) << endl; return 0; } |
Java
// Java Program to Check if binary representation // of a number is palindrome class GFG { // This function returns true if k'th bit in x // is set (or 1). For example if x (0010) is 2 // and k is 2, then it returns true static int isKthBitSet(long x, long k) { int rslt = ((x & (1 << (k - 1))) != 0) ? 1 : 0; return rslt; } // This function returns true if binary // representation of x is palindrome. // For example (1000...001) is paldindrome static int isPalindrome( long x) { long l = 1; // Initialize left position long r = (Integer.SIZE/8 )* 8; // initialize right position // One by one compare bits while (l < r) { if (isKthBitSet(x, l) != isKthBitSet(x, r)) { return 0; } l++; r--; } return 1; } // Driver Code public static void main (String[] args) { long x = 1 << 15 + 1 << 16 ; System.out.println(isPalindrome(x)); x = (1 << 31) + 1 ; System.out.println(isPalindrome(x)); } } // This code is contributed by AnkitRai01 |
Python3
# python 3 Program to Check if binary representation # of a number is palindrome import sys # This function returns true if k'th bit in x # is set (or 1). For example if x (0010) is 2 # and k is 2, then it returns true def isKthBitSet(x, k): if ((x & (1 << (k - 1))) !=0): return True else: return False # This function returns true if binary # representation of x is palindrome. # For example (1000...001) is paldindrome def isPalindrome(x): l = 1 # Initialize left position r = 2 * 8 # initialize right position # One by one compare bits while (l < r): if (isKthBitSet(x, l) != isKthBitSet(x, r)): return False l += 1 r -= 1 return True # Driver Code if __name__ =='__main__': x = 1 << 15 + 1 << 16 print(int(isPalindrome(x))) x = 1 << 31 + 1 print(int(isPalindrome(x))) # This code is contributed by # Surendra_Gangwar |
C#
// C# Program to Check if binary representation // of a number is palindrome using System; class GFG { // This function returns true if k'th bit in x // is set (or 1). For example if x (0010) is 2 // and k is 2, then it returns true static int isKthBitSet(long x, long k) { int rslt = ((x & (1 << (int)(k - 1))) != 0) ? 1 : 0; return rslt; } // This function returns true if binary // representation of x is palindrome. // For example (1000...001) is paldindrome static int isPalindrome( long x) { long l = 1; // Initialize left position long r = 4 * 8; // initialize right position // One by one compare bits while (l < r) { if (isKthBitSet(x, l) != isKthBitSet(x, r)) { return 0; } l++; r--; } return 1; } // Driver Code public static void Main () { long x = 1 << 15 + 1 << 16 ; Console.WriteLine(isPalindrome(x)); x = (1 << 31) + 1 ; Console.WriteLine(isPalindrome(x)); } } // This code is contributed by AnkitRai01 |
PHP
<?php // PHP Program to Check if binary representation // of a number is palindrome // This function returns true if k'th bit in x // is set (or 1). For example if x (0010) is 2 // and k is 2, then it returns true function isKthBitSet($x, $k) { return ($x & (1 << ($k - 1))) ? true : false; } // This function returns true if binary // representation of x is palindrome. // For example (1000...001) is paldindrome function isPalindrome($x) { $l = 1; // Initialize left position $r = sizeof(4) * 8; // initialize right position // One by one compare bits while ($l < $r) { if (isKthBitSet($x, $l) != isKthBitSet($x, $r)) return false; $l++; $r--; } return true; } // Driver Code $x = 1 << 15 + 1 << 16; echo isPalindrome($x), "\n"; $x = 1 << 31 + 1; echo isPalindrome($x), "\n"; // This code is contributed by ajit. ?> |
Output:
1 1
This article is contributed by Saurabh Gupta. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.
