QuestionC.java

package Q8_13_Stack_of_Boxes;

import java.util.ArrayList;
import java.util.Collections;

public class QuestionC {	
	public static int createStack(ArrayList<Box> boxes) {
		Collections.sort(boxes, new BoxComparator());
		int[] stackMap = new int[boxes.size()];
		return createStack(boxes, null, 0, stackMap);
	}
	
	public static int createStack(ArrayList<Box> boxes, Box bottom, int offset, int[] stackMap) {
		if (offset >= boxes.size()) {
			return 0;
		}
		
		/* height with this bottom */
		Box newBottom = boxes.get(offset);
		int heightWithBottom = 0;
		if (bottom == null || newBottom.canBeAbove(bottom)) {
			if (stackMap[offset] == 0) {
				stackMap[offset] = createStack(boxes, newBottom, offset + 1, stackMap);
				stackMap[offset] += newBottom.height;
			}
			heightWithBottom = stackMap[offset];
		}
		
		/* without this bottom */
		int heightWithoutBottom = createStack(boxes, bottom, offset + 1, stackMap);
		
		return Math.max(heightWithBottom, heightWithoutBottom);
	}
		
	
	public static void main(String[] args) {
		Box[] boxList = { new Box(6, 4, 4), new Box(8, 6, 2), new Box(5, 3, 3), new Box(7, 8, 3), new Box(4, 2, 2), new Box(9, 7, 3)};
		ArrayList<Box> boxes = new ArrayList<Box>();
		for (Box b : boxList) {
			boxes.add(b);
		}
		
		int height = createStack(boxes);
		System.out.println(height);
	}

}