text: Numbers in a Range with given Digital Root | C # implementation of the approach ; Function to return the count of required numbers ; Count of numbers present in given range ; Number of groups of 9 elements starting from L ; Left over elements not covered in factor 9 ; One Number in each group of 9 ; To check if any number in rem satisfy the property ; Driver code
code: using System ; class GFG { static int countNumbers ( int L , int R , int K ) { if ( K == 9 ) { K = 0 ; } int totalnumbers = R - L + 1 ; int factor9 = totalnumbers / 9 ; int rem = totalnumbers % 9 ; int ans = factor9 ; for ( int i = R ; i > R - rem ; i -- ) { int rem1 = i % 9 ; if ( rem1 == K ) { ans ++ ; } } return ans ; } public static void Main ( ) { int L = 10 ; int R = 22 ; int K = 3 ; Console . WriteLine ( countNumbers ( L , R , K ) ) ; } }