Digit Solitaire

Introduction

http://speedyguy17.info/data/mcpc/mcpc2012/pdf/B-Digit%20Solitaire.pdf

Despite the glorious fall colors in the midwest, there is a great deal of time to spend while on a train from St. Louis to Chicago. On a recent trip, we passed some time with the following game. We start with a positive integer S. So long as it has more than one digit, we compute the product of its digits and repeat. For example, if starting with 95, we compute 9 × 5 = 45. Since 45 has more than one digit, we compute 4 × 5 = 20. Continuing with 20, we compute 2 × 0 = 0. Having reached 0, which is a single-digit number, the game is over. As a second example, if we begin with 396, we get the following computations: 3 × 9 × 6 = 162 1 × 6 × 2 = 12 1 × 2 = 2 and we stop the game having reached 2.

Input: Each line contains a single integer 1 ≤ S ≤ 100000, designating the starting value. The value S will not have any leading zeros. A value of 0 designates the end of the input. Output: For each nonzero input value, a single line of output should express the ordered sequence of values that are considered during the game, starting with the original value.

Idea

This problem is quite easy; the idea is to write a function that checks the number of digits and the number, and then play the game. A more elegant way to check the number of digits is to convert it to a string and check the length.

Code

Solution - Java

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;

public class digits {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int counter = 1;
		while (true) {
			int next = scan.nextInt();
			if (next == 0) {
				break;
			}
			scan.nextLine();
			// System.out.print("Case " + counter + ":");
			ArrayList<Integer> input = new ArrayList<Integer>();
			input.add(next);
			ArrayList<Integer> list = play(input);
			Iterator<Integer> iter = list.iterator();
			while (iter.hasNext()) {
				System.out.print(iter.next());
				if (iter.hasNext()) {
					System.out.print(" ");
				}
			}
			System.out.println();
			counter++;
		}
	}

	private static ArrayList<Integer> play(ArrayList<Integer> in) {
		int last = in.get(in.size() - 1);
		if (length(last) > 1) {
			int product = 1;
			for (int i = length(last); i > 0; i--) {
				// System.out.println((int) Math.pow(10, i - 1));
				int digit = last / ((int) Math.pow(10, i - 1));
				product *= digit;
				last -= digit * (((int) Math.pow(10, i - 1)));
			}
			in.add(product);
			return play(in);
		} else {
			return in;
		}
	}

	private static int length(int in) {
		if (in == 100000) {
			return 6;
		} else if (in >= 10000) {
			return 5;
		} else if (in >= 1000) {
			return 4;
		} else if (in >= 100) {
			return 3;
		} else if (in >= 10) {
			return 2;
		} else {
			return 1;
		}
	}
}