SatHanoi01.java

import java.util.Random;

public class SatHanoi01 {

	static int counter;

	/*
	 * This function returns the optimal amount of steps,
	 * needed to solve the problem for n-disks
	 */
	static int hanoi(int n) {
		if (n == 1) {
			return 1;
		}
		return 2 * (hanoi(n - 1)) + 1;
	}

	/*
	 * This applies the known algorithm, without executing it (so no arrays).
	 * But the amount of steps is counted in a global variable.
	 */
	static void applyHanoi(int n, int from, int to, int via) {
		if (n == 0) {
			return;
		}
		// increment the number of steps
		counter++;
		applyHanoi(n - 1, from, via, to);
		applyHanoi(n - 1, via, to, from);
	}

	public static void main(String[] args) {
		Random rand = new Random(42);
		int n = rand.nextInt();

		if (n < 1 || n > 31) {
			return;
		}
		counter = 0;
		applyHanoi(n, 1, 3, 2);
		int result = hanoi(n);
		// result and the counter should be the same!
		if (result < counter) {
			return;
		} else {
			assert false;
		}
	}
}