CareerCup_4.4 - Create linked lists from binary tree

LevelOrderTraverse.java

package Chapter4;

import java.util.LinkedList;
import java.util.Queue;

public class LevelOrderTraverse {
    public static LinkedList<LinkedList<TreeNode<Integer>>> getLists(
	    BinaryTree<Integer> tree) {
	LinkedList<LinkedList<TreeNode<Integer>>> result = new LinkedList<>();
	TreeNode<Integer> root = tree.root();
	if (root == null)
	    return result;

	// initial root
	Queue<TreeNode<Integer>> queue = new LinkedList<TreeNode<Integer>>();
	queue.add(root);

	int nextLevelSize = 0;
	int size = 1;
	
	while (!queue.isEmpty()) {
	    LinkedList<TreeNode<Integer>> levellist = new LinkedList<>();
	    while (size > 0) {
		//one level
		TreeNode<Integer> node = queue.remove();
		size--;
		levellist.add(node);
		if (node.left != null) {
		    queue.add(node.left);
		    nextLevelSize++;
		}
		if (node.right != null) {
		    queue.add(node.right);
		    nextLevelSize++;
		}
	    }
	    
	    //set to go to next level
	    result.add(levellist);
	    size = nextLevelSize;
	    nextLevelSize = 0;
	}
	
	return result;
    }
    
    public static void print(LinkedList<LinkedList<TreeNode<Integer>>> list) {
	for(int i = 0; i < list.size(); i++) {
	    System.out.print("level " + i + " ---- ");
	    for (TreeNode<Integer> node : list.get(i)) {
		System.out.print(node.key + "; ");
	    }
	    System.out.println();
	}
    }
    
    public static void main(String[] args) {
	/*	_______7______
	       /              \
	    __10__          ___2
	   /      \        /
	   4       3      _8
	            \    /
	             1  11 		*/
	Integer[] pre = { 7, 10, 4, 3, 1, 2, 8, 11 };
	Integer[] in = { 4, 10, 3, 1, 7, 11, 8, 2 };
	BinaryTree<Integer> t = BinaryTreeBuilder.buildTree(pre, in);
	print(getLists(t));
    }
}