Check whether the number has only first and last bits set

• Difficulty Level : Easy
• Last Updated : 22 Mar, 2021

Given a positive integer n. The problem is to check whether only the first and last bits are set in the binary representation of n.
Examples:

Input : 9
Output : Yes
(9)10 = (1001)2, only the first and
last bits are set.

Input : 15
Output : No
(15)10 = (1111)2, except first and last
there are other bits also which are set.

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Approach: Following are the steps:

1. If n == 1, return “Yes”.
2. Else check whether n-1 is a power of 2. Refer this post.

C++

 // C++ to check whether the number has only// first and last bits set#include  using namespace std; // function to check whether 'n'// is a power of 2 or notbool powerOfTwo(unsigned int n){    return (!(n & n-1));} // function to check whether the number has only// first and last bits setbool onlyFirstAndLastAreSet(unsigned int n){    if (n == 1)        return true;    if (n == 2)        return false;    return powerOfTwo(n-1);   } // Driver program to test aboveint main(){    unsigned int n = 9;         if (onlyFirstAndLastAreSet(n))        cout << "Yes";    else        cout << "No";            return 0;}

Java

 // Java program to check whether the// number has only first and last// bits setimport java.util.*; class GFG{    // function to check whether 'n'    // is a power of 2 or not    static boolean powerOfTwo(int n)    {        return ((n & n - 1) == 0);    }     // function to check whether the number has     // only first and last bits set    static boolean onlyFirstAndLastAreSet(int n)    {        if (n == 1)            return true;             return powerOfTwo(n-1);    }     // Driver program to test above    public static void main (String[] args) {               int n = Integer.parseUnsignedInt("9");             if (onlyFirstAndLastAreSet(n))            System.out.println("Yes");        else            System.out.println("No");    }} /* This code is contributed by Mr. Somesh Awasthi */

Python3

 # Python3 program to check whether number# has only first and last bits set # function to check whether 'n'# is a power of 2 or notdef powerOfTwo (n):    return (not(n & n-1))  # function to check whether number # has only first and last bits setdef onlyFirstAndLastAreSet (n):     if (n == 1):        return True    return powerOfTwo (n-1) # Driver program to test aboven = 9if (onlyFirstAndLastAreSet (n)):    print('Yes')else:    print('No') # This code is contributed by Shariq Raza

C#

 // C# program to check whether the// number has only first and last// bits setusing System; class GFG {     // function to check whether 'n'    // is a power of 2 or not    static bool powerOfTwo(uint n)    {        return ((n & n - 1) == 0);    }     // function to check whether the number has    // only first and last bits set    static bool onlyFirstAndLastAreSet(uint n)    {        if (n == 1)            return true;         return powerOfTwo(n - 1);    }     // Driver program to test above    public static void Main()    {         uint n = (uint)9;         if (onlyFirstAndLastAreSet(n))            Console.WriteLine("Yes");        else            Console.WriteLine("No");    } } // This code is contributed by Sam007



Javascript



Output:

Yes

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