Number of n digit numbers that do not contain 9

Given a number n, find how many n digit number can be formed that does not contain 9 as it's digit.
Examples: 

Input : 1
Output : 8
Explanation :
Except 9, all numbers are possible

Input : 2
Output : 72
Explanation :
Except numbers from 90 - 99 and all
two digit numbers that does not end
with 9 are possible.

Total numbers of n digit number that can be formed will be 9*10^(n-1) as except first position all digits can be filled with 10 numbers (0-9). If a digit 9 is eliminated from the list then total number of n digit number will be 8*9^(n-1).

Below is the implementation of above idea: 

// CPP program to find number of n 
// digit numbers that do not 
// contain 9 as it's digit
#include <bits/stdc++.h>
using namespace std;

// function to find number of 
// n digit numbers possible 
int totalNumber(int n)
{
    return 8*pow(9, n - 1);
}

// driver function
int main()
{
    int n = 3;
    cout << totalNumber(n);
    return 0;
}

// Java program to find number of  
// n digit numbers that do not 
// contain 9 as it's digit
import java.io.*;

public class GFG
{
    
// function to find number of 
// n digit numbers possible 
static int totalNumber(int n)
{
    return 8 * (int)Math.pow(9, n - 1);
}

    // Driver Code
    static public void main (String[] args)
    {
        int n = 3;
        System.out.println(totalNumber(n));
        
    }
}

// This code is contributed by vt_m.

# python program to find number of n 
# digit numbers that do not 
# contain 9 as it's digit

# function to find number of 
# n digit numbers possible 
def totalNumber(n):
    
    return 8 * pow(9, n - 1);
 
# driver function
n = 3
print(totalNumber(n))

# This code is contributed by Sam007

// C# program to find number of  
// n digit numbers that do not 
// contain 9 as it's digit
using System;

public class GFG
{
    
// function to find number of 
// n digit numbers possible 
static int totalNumber(int n)
{
    return 8 * (int)Math.Pow(9, n - 1);
}

    // Driver Code
    static public void Main ()
    {
        int n = 3;
        Console.WriteLine(totalNumber(n));
        
    }
}

// This code is contributed by vt_m.

<?php
// php program to find number of n 
// digit numbers that do not 
// contain 9 as it's digit

// function to find number of 
// n digit numbers possible 
function totalNumber($n)
{
    return 8 * pow(9, $n - 1);
}
 
// driver function
$n = 3;
print(totalNumber($n))

// This code is contributed by Sam007
?>

<script>

// Javascript program to find number of  
// n digit numbers that do not 
// contain 9 as it's digit

// function to find number of 
// n digit numbers possible 
function totalNumber(n)
{
    return 8 * Math.pow(9, n - 1);
}
  
// Driver code
        let n = 3;
        document.write(totalNumber(n));
   
   // This code is contributed by code_hunt.
</script>

648

Time Complexity: O(log n)
Auxiliary Space: O(1)