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: 

C++

// 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

// 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.

Python3

# 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#

// 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
// 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
?>

Javascript

<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>

Output

648

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