Java Exercises: Reads n digits (given) chosen from 0 to 9 and prints the number of combinations

Java Basic: Exercise-228 with Solution

Write a Java program that reads n digits (given) chosen from 0 to 9 and prints the number of combinations where the sum of the digits equals to another given number (s). Do not use the same digits in a combination.

For example, the combinations where n = 3 and s = 6 are as follows:
1 + 2 + 3 = 6
0 + 1 + 5 = 6
0 + 2 + 4 = 6

Input:

Two integers as number of combinations and their sum by a single space in a line. Input 0 0 to exit.

Pictorial Presentation:

Sample Solution:

Java Code:

 import java.util.*;
public class Main {
    public static void main(String[] args) {
         Scanner stdIn = new Scanner(System.in);
		 System.out.println("Input number of combinations and sum (separated by a space in a line):"); 
         int n = stdIn.nextInt();
         int s = stdIn.nextInt();
         int c1 = comnum(0, n, s,0);
		 System.out.println("Number of combinations:");
         System.out.println(c1);
    }
    public static int comnum(int i, int n, int s,int p) {
        if(s == p && n == 0) {
            return 1;
        }
        if(i >= 10) {
            return 0;
        }
        if(n < 0) {
            return 0;
        }
 
        if(p > s) {
            return 0;
        }
        int c1 = comnum(i+1,n-1,s,p+i);
        int c2 = comnum(i+1,n,s,p);
        return c1+c2;
    }
}

Sample Output:

Input number of combinations and sum (separated by a space in a line):
3 6
Number of combinations:
3

Flowchart:

Java Code Editor:

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