Check whether the number has only first and last bits set
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.
Approach: Following are the steps:
- If n == 1, return “Yes”.
- Else check whether n-1 is a power of 2. Refer this post.
C++
#include <bits/stdc++.h>
using namespace std;
bool powerOfTwo(unsigned int n)
{
return (!(n & n-1));
}
bool onlyFirstAndLastAreSet(unsigned int n)
{
if (n == 1)
return true ;
if (n == 2)
return false ;
return powerOfTwo(n-1);
}
int main()
{
unsigned int n = 9;
if (onlyFirstAndLastAreSet(n))
cout << "Yes" ;
else
cout << "No" ;
return 0;
}
|
Java
import java.util.*;
class GFG
{
static boolean powerOfTwo( int n)
{
return ((n & n - 1 ) == 0 );
}
static boolean onlyFirstAndLastAreSet( int n)
{
if (n == 1 )
return true ;
return powerOfTwo(n- 1 );
}
public static void main (String[] args) {
int n = Integer.parseUnsignedInt( "9" );
if (onlyFirstAndLastAreSet(n))
System.out.println( "Yes" );
else
System.out.println( "No" );
}
}
|
Python3
def powerOfTwo (n):
return ( not (n & n - 1 ))
def onlyFirstAndLastAreSet (n):
if (n = = 1 ):
return True
return powerOfTwo (n - 1 )
n = 9
if (onlyFirstAndLastAreSet (n)):
print ( 'Yes' )
else :
print ( 'No' )
|
C#
using System;
class GFG {
static bool powerOfTwo( uint n)
{
return ((n & n - 1) == 0);
}
static bool onlyFirstAndLastAreSet( uint n)
{
if (n == 1)
return true ;
return powerOfTwo(n - 1);
}
public static void Main()
{
uint n = ( uint )9;
if (onlyFirstAndLastAreSet(n))
Console.WriteLine( "Yes" );
else
Console.WriteLine( "No" );
}
}
|
PHP
<?php
function powerOfTwo( $n )
{
return (!( $n & $n - 1));
}
function onlyFirstAndLastAreSet( $n )
{
if ( $n == 1)
return true;
if ( $n == 2)
return false;
return powerOfTwo( $n - 1);
}
$n = 9;
if (onlyFirstAndLastAreSet( $n ))
echo "Yes" ;
else
echo "No" ;
?>
|
Javascript
<script>
function powerOfTwo(n)
{
return (!(n & n-1));
}
function onlyFirstAndLastAreSet(n)
{
if (n == 1)
return true ;
if (n == 2)
return false ;
return powerOfTwo(n-1);
}
var n = 9;
if (onlyFirstAndLastAreSet(n))
document.write( "Yes" );
else
document.write( "No" );
</script>
|
Output:
Yes
Time Complexity – O(1)
Space Complexity – O(1)
Last Updated :
21 Jun, 2022
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