二叉树创建及其遍历方式

package com.linkedlist.exe.com.tree.exe;

import java.util.Arrays;
import java.util.LinkedList;

/**
 * @program: Aglorithm
 * @Date: ******
 * @Author: Kyrie
 * @Description: 用链表(递归)创建二叉树，前中后序进行(递归)遍历
 * 递归方式：借助于栈比较好理解
 */
//定义树的结点
class Node{
    public Node left;
    public Node right;
    public int data;
    public Node(){
    }
    public Node(int data){
        this.data = data;
    }
}

public class Demo1_BianryTree {
    //创建二叉树
    public static Node createBinaryTree(LinkedList<Integer> list){
        if(list == null || list.size() == 0){
            return null;
        }
        //从链表的头部移除结点
        Integer data = list.removeFirst();
        Node node = null;
        if(data != null){  //如果不为空,则创建Node结点
            node = new Node(data); //根节点
            node.left = createBinaryTree(list);  //创建左子树  通过栈来比较好理解  最后返回根结点
            node.right = createBinaryTree(list);  //创建右子树
        }

        return node;
    }
    //前序遍历：根节点->左子树->右子树
    public static void prePrint(Node node){
        if(node != null){
            System.out.println(node.data);
            prePrint(node.left);
            prePrint(node.right);
        }
    }
    //中序遍历：左子树->根节点->右子树
    public static void midPrint(Node node){
        if(node != null){
            midPrint(node.left);
            System.out.println(node.data);
            midPrint(node.right);
        }
    }
    //后序遍历：左子树->右子树->根节点
    public static void afterPrint(Node node){
        if(node != null){
            afterPrint(node.left);
            afterPrint(node.right);
            System.out.println(node.data);
        }
    }
    public static void main(String[] args) {
        LinkedList<Integer> list = new LinkedList<>(Arrays.asList(
                new Integer[]{1,2,4,null,null,5,null,null,3,null,6,null,null}));
        //创建二叉树
        Node treeNode = createBinaryTree(list);
        //前序遍历
        prePrint(treeNode);
        System.out.println("===========");
        //中序遍历
        midPrint(treeNode);
        System.out.println("===========");

        //后序遍历
        afterPrint(treeNode);
        System.out.println("===========");

    }
}