[leetcode]Binary Tree Zigzag Level Order Traversal - java

这个提跟Binary Tree Level Order Traversal 一样，只是结果集用栈

/**

 * Definition for binary tree

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

public class Solution {

   public List<List<Integer>> zigzagLevelOrder(TreeNode root) {

        List<List<Integer>> result = new ArrayList<List<Integer>>();

        if(root == null){

            return result;

        }

        List<Integer> first = new ArrayList<Integer>();

        first.add(root.val);

        result.add(first);



        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();

        LinkedList<TreeNode> childrenQueue = new LinkedList<TreeNode>();

        queue.add(root);

        int i =1;

        while (!queue.isEmpty()) {

            TreeNode node = queue.remove();

            if(node.left!=null){

                childrenQueue.add(node.left);

            }

            if(node.right!=null){

                childrenQueue.add(node.right);

            }

            if(queue.isEmpty() && !childrenQueue.isEmpty()){

                queue.addAll(childrenQueue);

                LinkedList<Integer> childrenResult = new LinkedList<Integer>();

                boolean flag = i%2==0?true:false;

                for(TreeNode child : childrenQueue){

                    if(flag){

                        childrenResult.add(child.val);

                    }else{

                        childrenResult.push(child.val);

                    }

                }

                result.add(childrenResult);

                childrenQueue.clear();

                i++;

            }

        }

        return result;

    }

}