leetcode：二叉树遍历（递归）

package com.lz.second;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class BinaryTree {
	public static class TreeNode{
		int val;
		TreeNode left;
		TreeNode right;
		int deep;
		TreeNode(int val,TreeNode left,TreeNode right){
			this.val=val;
			this.left=left;
			this.right=right;
		}
	}
	
	private static List list=new ArrayList<>();
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeNode node7 = new TreeNode(7,null,null); 
		TreeNode node6 = new TreeNode(6,null,null); 
		TreeNode node5 = new TreeNode(5,node6,node7); 
		TreeNode node4 = new TreeNode(4,null,null); 
		TreeNode node3 = new TreeNode(3,null,null); 
		TreeNode node2 = new TreeNode(2,node4,node5); 
		TreeNode node1 = new TreeNode(1,node2,node3); 
		//preorder(node1);
		//inorder(node1);
		//postorder(node1);
		levelorder(node1,1);
		System.out.println(Arrays.toString(list.toArray()));
	}

	//前序144
	public static void preorder(TreeNode root) {
		if(root==null) {
			return;
		}
		System.out.println(root.val);//第一次成为栈顶元素打印
		preorder(root.left);
		preorder(root.right);
	}
	
	
	//中序
	public static void inorder(TreeNode root) {
		if(root==null) {
			return;
		}
		inorder(root.left);
		System.out.println(root.val);//第二次成为栈顶元素打印
		inorder(root.right);
	}
	
	
	//后序
	public static void postorder(TreeNode root) {
		if(root==null) {
			return;
		}
		postorder(root.left);
		postorder(root.right);
		System.out.println(root.val);//第三次成为栈顶元素打印
	}
	
	
	//层序遍历
	public static void levelorder(TreeNode root,int i) {
		if(root==null) {
			return;
		}
		int length=list.size();
		if(length<=i) {
			for(int j=0;j<=i-length;j++) {
				list.add(length+j,null);
			}
		}
		list.set(i,root.val);
		levelorder(root.left,2*i);
		levelorder(root.right,2*i+1);
	}	
		
}