import java.util.Arrays;
import java.util.HashSet;
import java.util.InputMismatchException;
import java.util.Scanner;

/**
 * Class for converting from "any" base to "any" other base, when "any" means from 2-36.
 * Works by going from base 1 to decimal to base 2. Includes auxiliary method for 
 * determining whether a number is valid for a given base.
 * 
 * @author Michael Rolland
 * @version 2017.10.10
 *
 */
public class AnyBaseToAnyBase {
	
	// Smallest and largest base you want to accept as valid input
	static final int MINIMUM_BASE = 2;
	static final int MAXIMUM_BASE = 36;
	
	// Driver
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		String n;
		int b1=0,b2=0;
		while (true) {
			try {
				System.out.print("Enter number: ");
				n = in.next();
				System.out.print("Enter beginning base (between "+MINIMUM_BASE+" and "+MAXIMUM_BASE+"): ");
				b1 = in.nextInt();
				if (b1 > MAXIMUM_BASE || b1 < MINIMUM_BASE) {
					System.out.println("Invalid base!");
					continue;
				}
				if (!validForBase(n, b1)) {
					System.out.println("The number is invalid for this base!");
					continue;
				}
				System.out.print("Enter end base (between "+MINIMUM_BASE+" and "+MAXIMUM_BASE+"): ");
				b2 = in.nextInt();
				if (b2 > MAXIMUM_BASE || b2 < MINIMUM_BASE) {
					System.out.println("Invalid base!");
					continue;
				}
				break;
			} catch (InputMismatchException e) {
				System.out.println("Invalid input.");
				in.next();
			}
		}
		System.out.println(base2base(n, b1, b2));
	}
	
	/**
	 * Checks if a number (as a String) is valid for a given base.
	 */
	public static boolean validForBase(String n, int base) {
		char[] validDigits = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E',
				'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
				'W', 'X', 'Y', 'Z'};
		// digitsForBase contains all the valid digits for the base given
		char[] digitsForBase = Arrays.copyOfRange(validDigits, 0, base);
		
		// Convert character array into set for convenience of contains() method
		HashSet digitsList = new HashSet();
		for (int i=0; i= 'A' && charB1 = 10, add a character with the
			// corresponding value to the new number. (A = 10, B = 11, C = 12, ...)
			else
				output = (char)((decimalValue % b2)+55) + output;
			// Divide by the new base again
			decimalValue /= b2;
		}
		return output;
	}
}