QuestionC.java

package Question17_13;


public class QuestionC {

	public static void printAsTree(BiNode root, String spaces) {
		if (root == null) {
			System.out.println(spaces + "- null");
			return;
		}
		System.out.println(spaces + "- " + root.data);
		printAsTree(root.node1, spaces + "   ");
		printAsTree(root.node2, spaces + "   ");
	}
	
	public static BiNode createTree() {
		BiNode[] nodes = new BiNode[7];
		for (int i = 0; i < nodes.length; i++) {
			nodes[i] = new BiNode(i);
		}
		nodes[4].node1 = nodes[2];
		nodes[4].node2 = nodes[5];
		nodes[2].node1 = nodes[1];
		nodes[2].node2 = nodes[3];
		nodes[5].node2 = nodes[6];
		nodes[1].node1 = nodes[0];
		return nodes[4];
	}
	
	public static void printLinkedListTree(BiNode root) {
		for (BiNode node = root; node != null; node = node.node2) {
			if (node.node2 != null && node.node2.node1 != node) {
				System.out.print("inconsistent node: " + node);
			}
			System.out.print(node.data + "->");
		}
		System.out.println();
	}
	
	public static BiNode convertToCircular(BiNode root) {
		if (root == null) {
			return null;
		}
		
		BiNode part1 = convertToCircular(root.node1);
		BiNode part3 = convertToCircular(root.node2);
				
		if (part1 == null && part3 == null) {
			root.node1 = root;
			root.node2 = root;
			return root;
		}
		BiNode tail3 = part3 == null ? null : part3.node1;
		
		/* join left to root */
		if (part1 == null) {
			concat(part3.node1, root);
		} else {
			concat(part1.node1, root);
		}
		
		/* join right to root */
		if (part3 == null) {
			concat(root, part1);
		} else {
			concat(root, part3);
		}
		
		/* join right to left */
		if (part1 != null && part3 != null) {
			concat(tail3, part1);
		}
		
		return part1 == null ? root : part1;
	}
	
	public static BiNode convert(BiNode root) {
		BiNode head = convertToCircular(root);
		head.node1.node2 = null;
		head.node1 = null;
		return head;
	}
	
	public static void concat(BiNode x, BiNode y) {
		x.node2 = y;
		y.node1 = x;
	}
	
	public static void main(String[] args) {
		BiNode root = createTree();
		printAsTree(root, "");
		BiNode r = convert(root);
		printLinkedListTree(r);
	}

}