剑指offer(五十三)之按之字形顺序打印二叉树

Posted 2020-07-24 奔跑着的国风

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>