打印二叉树

按之字形顺序打印二叉树

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Stack;
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        
        ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
        if(pRoot==null) return results;
        Stack<TreeNode> oddStack = new Stack<TreeNode>();
        Stack<TreeNode> evenStack =new Stack<TreeNode>();
        int flag=0;
        oddStack.push(pRoot);
        while(!oddStack.isEmpty()||!evenStack.isEmpty()){
            ArrayList<Integer> list = new ArrayList<Integer>();
            if(flag%2==0){
                while(!oddStack.isEmpty()){
                    TreeNode tNode = oddStack.pop();
                    list.add(tNode.val);
                    if(tNode.left!=null) evenStack.push(tNode.left);
                    if(tNode.right!=null) evenStack.push(tNode.right);
                }
            }else{
                while(!evenStack.isEmpty()){
                    TreeNode tNode = evenStack.pop();
                    list.add(tNode.val);
                    if(tNode.right!=null) oddStack.push(tNode.right);
                    if(tNode.left!=null) oddStack.push(tNode.left);
                }
            }
            flag++;
            results.add(list);
        }
        return results;
    }

}

把二叉树打印成多行

从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
        if(pRoot==null) return results;
        Queue<TreeNode> que = new LinkedList<TreeNode>();
        Queue<TreeNode> que2 = new LinkedList<TreeNode>();
        int flag=0;
        que.offer(pRoot);
        while(!que.isEmpty()||!que2.isEmpty()){
            ArrayList<Integer> list = new ArrayList<Integer>();
            if(flag%2==0){
                while(!que.isEmpty()){
                    TreeNode tNode = que.poll();
                    list.add(tNode.val);
                    if(tNode.left!=null) que2.offer(tNode.left);
                    if(tNode.right!=null) que2.offer(tNode.right);
                }
            }else{
                while(!que2.isEmpty()){
                    TreeNode tNode = que2.poll();
                    list.add(tNode.val);
                    if(tNode.left!=null) que.offer(tNode.left);
                    if(tNode.right!=null) que.offer(tNode.right);
                }   
            }
            flag++;
            results.add(list);
        }
        return results;
    }
    
}