Find the number of integers from 1 to n which contains digits 0’s and 1’s only

Given a number N. The task is to find the number of integers from 1 to n which contains digits 0’s and 1’s only.

Examples:

Input : N = 15
Output : 3
Explanation : 1, 10, 11 are such integers.

Input : N = 120
Output : 7
Explanation : 1, 10, 11, 100, 101, 110, 111 
are such integers.

Approach: An efficient approach is to build integers which contain 1’s and 0’s only using a recursive function starting from the number 1. For each number check whether it is less than n or not.

Below is the implementation of the above approach:

C++

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// CPP program to find the number of integers
// from 1 to n which contains digits 0's and 1's only
  
#include <bits/stdc++.h>
using namespace std;
  
// Function to find the number of integers
// from 1 to n which contains 0's and 1's only
int countNumbers(int x, int n)
{
    // If number is greater than n
    if (x > n)
        return 0;
  
    // otherwise add count this number and
    // call two functions
    return 1 + countNumbers(x * 10, n) + countNumbers(x * 10 + 1, n);
}
  
// Driver code
int main()
{
    int n = 120;
  
    cout << countNumbers(1, n);
  
    return 0;
}

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Java














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// Java program to find the number of integers 


// from 1 to n which contains digits 0's and 1's only 


class GFG 


{ 


      


// Function to find the number of integers 


// from 1 to n which contains 0's and 1's only 


static int countNumbers(int x, int n) 


{ 


    // If number is greater than n 


    if (x > n) 


        return 0; 


  


    // otherwise add count this number and 


    // call two functions 


    return 1 + countNumbers(x * 10, n) + countNumbers(x * 10 + 1, n); 


} 


  


// Driver code 


public static void main (String[] args)  


{ 


    int n = 120; 


  


    System.out.println(countNumbers(1, n)); 


} 


} 


  


// This code is contributed by chandan_jnu 



















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Python3














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# Python3 program to find the number of  


# integers from 1 to n which contains  


# digits 0's and 1's only  


  


# Function to find the number of integers  


# from 1 to n which contains 0's and 1's only  


def countNumbers(x, n):  


      


    # If number is greater than n  


    if x > n :  


        return 0


  


    # otherwise add count this number and  


    # call two functions  


    return (1 + countNumbers(x * 10, n) + 


                countNumbers(x * 10 + 1, n))  


  


# Driver code  


if __name__ == '__main__':  


    n = 120;  


  


    print(countNumbers(1, n)); 


      


# This code is contributed by Arnab Kundu 



















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C#














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// C# program to find the number of integers  


// from 1 to n which contains digits 0's and 1's only  


using System; 


  


class GFG  


{  


  


// Function to find the number of integers  


// from 1 to n which contains 0's and 1's only  


static int countNumbers(int x, int n)  


{  


    // If number is greater than n  


    if (x > n)  


        return 0;  


  


    // otherwise add count this number and  


    // call two functions  


    return 1 + countNumbers(x * 10, n) +  


               countNumbers(x * 10 + 1, n);  


}  


  


// Driver code  


public static void Main()  


{  


    int n = 120;  


  


    Console.WriteLine(countNumbers(1, n));  


}  


}  


  


// This code is contributed by Ryuga 



















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PHP














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<?php 


// PHP program to find the number of  


// integers from 1 to n which contains 


// digits 0's and 1's only 


  


// Function to find the number of integers 


// from 1 to n which contains 0's and 1's only 


function countNumbers($x, $n) 


{ 


    // If number is greater than n 


    if ($x > $n) 


        return 0; 


  


    // otherwise add count this number and 


    // call two functions 


    return 1 + countNumbers($x * 10, $n) +  


               countNumbers($x * 10 + 1, $n); 


} 


  


// Driver code 


$n = 120; 


  


echo(countNumbers(1, $n)); 


  


// This code is contributed  


// by Code_Mech. 


?> 



















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Output:


7






          
          
          
          

            

    

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