剑指offer(五十三)之按之字形顺序打印二叉树

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题目描述

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。

代码：

<span style="color:#000099;">import java.util.ArrayList;import java.util.*;/*public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class Solution {    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();        if(pRoot == null){            return result;        }        boolean leftToRight = true;        Queue<TreeNode> layer = new LinkedList<TreeNode>();        ArrayList<Integer> layerList = new ArrayList<Integer>();        layer.add(pRoot);        int start = 0, end = 1;        while(!layer.isEmpty()){            TreeNode cur = layer.remove();            layerList.add(cur.val);            start++;            if(cur.left!=null){                layer.add(cur.left);                      }            if(cur.right!=null){                layer.add(cur.right);            }            if(start == end){                end = layer.size();                start = 0;                             if(!leftToRight){                    result.add(reverse(layerList));                }else{                    result.add(layerList);                }                leftToRight = !leftToRight;                layerList = new ArrayList<Integer>();            }        }        return result;    }    private ArrayList reverse(ArrayList<Integer> layerList) {            int length = layerList.size();        ArrayList<Integer> reverseList = new ArrayList<Integer>();        for(int i = length-1; i >= 0;i--){            reverseList.add(layerList.get(i));        }        return reverseList;    }}</span>

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