Same Number Of Set Bits As N

Given a positive integer N, find out how many positive integers strictly less than N have the same number of set bits as N.

Examples :

Input : 8
Output :3
Explanation: Binary representation of
8 : 1000, so number of set bits in 8 is 1.
So the integers less than 8 with same number 
of set bits are : 4, 2, 1

Input :1
Output :0

Input :4
Output :2

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

1. Using __builtin_popcount() inbuilt function, count set bits in N and store into a 
temp variable 
2. Iterate from n-1 to 1 and also count set bits in i using __builtin_popcount() 
function
3. Now, compare temp with __builtin_popcount(i)
4. If both are equal then increment counter variable
5. Return counter

Below is the implementation of above approach.

C++

// CPP program to find numbers less than N 
// that have same Number Of Set Bits As N 
#include <iostream> 
using namespace std; 
  
int smallerNumsWithSameSetBits(int n) 
{         
    // __builtin_popcount function that count 
    // set bits in n 
    int temp = __builtin_popcount(n); 
      
    // Iterate from n-1 to 1 
    int count = 0; 
    for (int i = n - 1; i > 0; i--) { 
          
        // check if the number of set bits  
        // equals to temp increment count         
        if (temp == __builtin_popcount(i)) 
            count++; 
    } 
    return count; 
} 
  
// Driver Code  
int main() 
{ 
    int n = 4; 
    cout << smallerNumsWithSameSetBits(n); 
    return 0; 
} 

Java

// Java program to find numbers less than N 
// that have same Number Of Set Bits As N 
class GFG { 
      
    // returns number of set bits in a number 
    static int __builtin_popcount(int n) 
    { 
        int d, t = 0; 
          
        while(n > 0) 
        { 
            d = n % 2; 
            n = n / 2; 
            if(d == 1) 
                t++; 
        } 
        return t; 
    } 
      
    static int smallerNumsWithSameSetBits(int n) 
    {      
        // __builtin_popcount function that count 
        // set bits in n 
        int temp = __builtin_popcount(n); 
          
        // Iterate from n-1 to 1 
        int count = 0; 
        for (int i = n - 1; i > 0; i--) { 
              
            // check if the number of set bits  
            // equals to temp increment count      
            if (temp == __builtin_popcount(i)) 
                count++; 
        } 
        return count; 
    } 
      
    // Driver Code  
    public static void main(String[] args) 
    { 
        int n = 4; 
        System.out.println( 
            smallerNumsWithSameSetBits(n)); 
    } 
} 
  
// This code is contributed by Arnab Kundu. 

Python3

# Python3 program to find numbers  
# less than N that have same 
# Number Of Set Bits As N 
def __builtin_popcount(n) : 
    t = 0    
    while(n > 0) : 
        d = n % 2
        n = int(n / 2) 
        if(d == 1) : 
            t = t + 1
    return t 
  
def smallerNumsWithSameSetBits(n) :     
      
    # __builtin_popcount function  
    # that count set bits in n 
    temp = __builtin_popcount(n) 
      
    # Iterate from n-1 to 1 
    count = 0
    for i in range(n-1,0,-1) :      
          
        # check if the number of  
        # set bits equals to temp 
        # increment count      
        if (temp == __builtin_popcount(i)) : 
            count = count + 1
    return count 
  
# Driver Code  
n = 4
print (smallerNumsWithSameSetBits(n)) 
  
# This code is contributed by  
# Manish Shaw(manishshaw1) 

C#

// C# program to find numbers less than N 
// that have same Number Of Set Bits As N 
using System; 
  
class GFG { 
      
    // returns number of set bits in a number 
    static int __builtin_popcount(int n) 
    { 
        int d, t = 0; 
           
        while(n > 0) 
        { 
            d = n % 2; 
            n = n / 2; 
            if(d == 1) 
                t++; 
        } 
        return t; 
    } 
      
    static int smallerNumsWithSameSetBits(int n) 
    {      
        // __builtin_popcount function that count 
        // set bits in n 
        int temp = __builtin_popcount(n); 
          
        // Iterate from n-1 to 1 
        int count = 0; 
        for (int i = n - 1; i > 0; i--) { 
              
            // check if the number of set bits  
            // equals to temp increment count      
            if (temp == __builtin_popcount(i)) 
                count++; 
        } 
        return count; 
    } 
      
    // Driver Code  
    static public void Main(String []args) 
    { 
        int n = 4; 
        Console.WriteLine( 
            smallerNumsWithSameSetBits(n)); 
    } 
} 
  
// This code is contributed by Arnab Kundu. 

PHP

<?php 
// PHP program to find numbers  
// less than N that have same 
// Number Of Set Bits As N 
function __builtin_popcount($n) 
{ 
    $t = 0;      
    while($n > 0) 
    { 
        $d = $n % 2; 
        $n = intval($n / 2); 
        if($d == 1) 
            $t++; 
    } 
    return $t; 
} 
function smallerNumsWithSameSetBits($n) 
{      
    // __builtin_popcount function  
    // that count set bits in n 
    $temp = __builtin_popcount($n); 
      
    // Iterate from n-1 to 1 
    $count = 0; 
    for ($i = $n - 1; $i > 0; $i--) 
    { 
          
        // check if the number of  
        // set bits equals to temp 
        // increment count      
        if ($temp == __builtin_popcount($i)) 
            $count++; 
    } 
    return $count; 
} 
  
// Driver Code  
$n = 4; 
echo (smallerNumsWithSameSetBits($n)); 
  
// This code is contributed by  
// Manish Shaw(manishshaw1) 
?> 

Output:

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

PHP

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