递归2——二叉树前序遍历、中序遍历、后序遍历、层次遍历

import java.util.LinkedList;
import java.util.Queue;

public class Recursion3 {
    public static void main(String[] args) {
        Recursion3 recursion3 = new Recursion3();
        recursion3.buildTree();
    }

    public void buildTree() {
        TreeNode root = new TreeNode(0);
        TreeNode node1 = new TreeNode(1);
        TreeNode node2 = new TreeNode(2);
        TreeNode node3 = new TreeNode(3);
        TreeNode node4 = new TreeNode(4);
        TreeNode node5 = new TreeNode(5);
        TreeNode node6 = new TreeNode(6);
        TreeNode node7 = new TreeNode(7);
        TreeNode node8 = new TreeNode(8);

        root.setLeft(node1);
        root.setRight(node2);

        node1.setLeft(node3);
        node1.setRight(node4);

        nod