// CSE 143, Winter 2011, Marty Stepp
// This program uses recursive backtracking to solve the problem of whether
// a group of dominoes can be lined up to produce a chain that starts and ends
// with a particular number.

import static org.junit.Assert.*;
import org.junit.*;
import java.util.*;

public class DominoesTest {
	// Returns true if a chain of dominoes can be made from the given list
	// that starts and ends with the given numbers. Otherwise returns false.
	// Assumes that if start == end, it's trivial, so we should return true.
	// Precondition: 0 <= start,end <= 6
	// Precondition: dominoes != null
	public boolean hasChain(List<Domino> dominoes, int start, int end) {
		
		if (start == end) {
			return true;       // base case
		} else {
			// start != end
			for (int i = 0; i < dominoes.size(); i++) {
				// choose: pick a domino to start the chain
				Domino d = dominoes.get(i);
				if (d.contains(start)) {    // d.first() or d.last() is start
					dominoes.remove(i);                          // choose
					if (d.second() == start) {
						d.flip();
					}
					if (hasChain(dominoes, d.second(), end)) {   // explore
						return true;
					}
					dominoes.add(i, d);                          // un-choose
				}
			}
			return false;   // tried all dominoes and none worked
		}
	}
	
	@Test
	public void test1() {
		helper(5, 5, true);
	}
	
	@Test
	public void test2() {
		helper(1, 5, true);
	}
	
	@Test
	public void test3() {
		helper(1, 3, true);
	}
	
	@Test
	public void test4() {
		helper(1, 6, false);
	}
	
	@Test
	public void test5() {
		helper(1, 2, false);
	}
	
	// helper for all of the JUnit test cases
	private void helper(int start, int end, boolean expected) {
		List<Domino> dominoes = new ArrayList<Domino>();
		dominoes.add(new Domino(1, 4));
		dominoes.add(new Domino(2, 6));
		dominoes.add(new Domino(4, 5));
		dominoes.add(new Domino(1, 5));
		dominoes.add(new Domino(3, 5));
		
		boolean actual = hasChain(new ArrayList<Domino>(dominoes), start, end);
		assertEquals("chain from " + start + " to " + end, expected, actual);
	}
}