text: Count n digit numbers not having a particular digit | C # Implementation of above method ; Finding number of possible number with n digits excluding a particular digit ; Checking if number of digits is zero ; Checking if number of digits is one ; Checking if number of digits is odd ; Calling digitNumber function with ( digit - 1 ) / 2 digits ; Calling digitNumber function with n / 2 digits ; Calling digitNumber function Checking if excluding digit is zero or non - zero ; Driver function to run above program ; Initializing variables
code: using System ; class GFG { static int mod = 1000000007 ; static int digitNumber ( long n ) { if ( n == 0 ) return 1 ; if ( n == 1 ) return 9 ; if ( n % 2 != 0 ) { int temp = digitNumber ( ( n - 1 ) / 2 ) % mod ; return ( 9 * ( temp * temp ) % mod ) % mod ; } else { int temp = digitNumber ( n / 2 ) % mod ; return ( temp * temp ) % mod ; } } static int countExcluding ( int n , int d ) { if ( d == 0 ) return ( 9 * digitNumber ( n - 1 ) ) % mod ; else return ( 8 * digitNumber ( n - 1 ) ) % mod ; } public static void Main ( ) { int d = 9 ; int n = 3 ; Console . WriteLine ( countExcluding ( n , d ) ) ; } }