尝试不同方法求二叉树的深度：

1.depth1，递归计算二叉树的深度，根结点的深度=max(左子树的深度，右子树的深度) + 1。

2.depth2，访问左结点，如有右结点则压栈1，同时把右结点的深度压栈2，没有左结点时表示该次遍历完成，记录深度；从栈1取出结点，栈2取出该结点的深度，再次遍历。

3.depth3，利用层序遍历的思想，每完成一层的遍历就给一个标记。

package com.devchao.tree;

import java.util.LinkedList;

import java.util.Queue;

import java.util.Stack;

public class BinaryTree {

public static void main(String[] args) {

Node n15 = new Node(15, null, null);

Node n14 = new Node(14, n15, null);

Node n13 = new Node(13, null, n14);

Node n12 = new Node(12, n13, null);

Node n11 = new Node(11, null, n12);

Node n5 = new Node(5, null, null);

Node n6 = new Node(6, null, null);

Node n8 = new Node(8, null, null);

Node n9 = new Node(9, n11, null);

Node n10 = new Node(10, null, null);

Node n7 = new Node(7, n8, null);

Node n4 = new Node(4, n6, n7);

Node n3 = new Node(3, null, n5);

Node n2 = new Node(2, n9, n10);

Node n1 = new Node(1, n3, n4);

Node root = new Node(0, n1, n2);

System.out.println(depth3(root));

}

public static int depth1(Node root){

int dep1 = 1, dep2 = 1;

if(root.left != null) {

dep1 = dep1 + depth1(root.left);

}

if(root.right != null) {

dep2 = dep2 + depth1(root.right);

}

System.out.println(root.data + " " + dep1 + " " + dep2);

return dep1 >= dep2 ? dep1 : dep2;

}

public static int depth2(Node root){

int dep = 1, tempDep = 1;

Stack q = new Stack();

Stack dq = new Stack();

Node node = root;

while(node != null || !q.isEmpty()) {

if(node == null) {

node = q.pop();

dep = dep < tempDep ? tempDep : dep;

tempDep = dq.pop();

}

if(node.right != null) {

dq.add(tempDep + 1);

q.add(node.right);

}

if(node.left != null) {

tempDep = tempDep + 1;

}

node = node.left;

}

return dep;

}

public static int depth3(Node root){

int dep = 0, tempTag = 0;

Queue queue = new LinkedList<>();

queue.add(root);

Queue tagQueue = new LinkedList<>();

tagQueue.add(1);

while(!queue.isEmpty()) {

root = queue.poll();

if(root.left != null) {

queue.add(root.left);

tagQueue.add(0);

}

if(root.right != null) {

queue.add(root.right);

tagQueue.add(0);

}

tempTag = tagQueue.poll();

if(tempTag == 1) {

dep = dep + 1;

if(!tagQueue.isEmpty()) {

tagQueue.remove();

tagQueue.add(1);

}

}

}

return dep;

}

static class Node {

public int data;

public Node left;

public Node right;

public Node(int data, Node left, Node right) {

this.data = data;

this.left = left;

this.right = right;

}

}

}