二叉树遍历

package com.exe4.offer;

import java.util.Stack;

/**
* 前序、中序、后序遍历方法
* @author WGS
*
*/
public class BianliOfBinarryTree {
public static class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
this.val = val;

}
}
/**
* 方法一：大话数据结构中简便方法，可实现操作。
* @param args
*/

public void preOrder(TreeNode node){
if(node==null) return;
System.out.print(node.val+" ");
preOrder(node.left);
preOrder(node.right);
}
public void inOrder(TreeNode node){
if(node==null) return;
inOrder(node.left);
System.out.print(node.val+" ");
inOrder(node.right);
}
public void postOrder(TreeNode node){
if(node==null) return;
postOrder(node.left);
postOrder(node.right);
System.out.print(node.val+" ");
}
/**
* 方法二：剑指offer中的方法：加入栈操作
* @param args
*/
public void preOrder2(TreeNode node){
Stack<TreeNode> stack=new Stack<TreeNode>();

while(node!=null || !stack.empty()){
//先遍历左子树
while(node!=null){
System.out.print(node.val+" ");
stack.push(node);
node=node.left;//左子树遍历结束后，node==null,跳出此循环
}
//左子树遍历结束，继续遍历右子树
if(!stack.isEmpty()){
node=stack.pop();//一直返回，直到根节点处，node==null，即stack==isEmpty()
node=node.right;
}
}
}
public void inOrder2(TreeNode node){
Stack<TreeNode> stack=new Stack<TreeNode>();
while(node!=null || !stack.isEmpty()){

while(node!=null){
stack.push(node);//8 6 5
node=node.left; //6 5 null
}

if(!stack.isEmpty()){
node=stack.pop();//5 6
System.out.print(node.val+" ");//5 6
node=node.right;//null
}
}
}
//后序遍历暂时还不会
/*public void postOrder2(TreeNode node){
Stack<TreeNode> stack=new Stack<TreeNode>();
while(node!=null || !stack.isEmpty()){
while(node!=null){
stack.push(node);//8 6 5 7
node=node.left;//6 5 null null
}
if(!stack.isEmpty()){
node=stack.pop();//5 6 7
node=node.right;//null 7 null

}

}
}*/

public static void main(String[] args) {
TreeNode root = new TreeNode(8);
TreeNode node1 = new TreeNode(6);
TreeNode node2 = new TreeNode(10);
TreeNode node3 = new TreeNode(5);
TreeNode node4 = new TreeNode(7);
TreeNode node5 = new TreeNode(9);
TreeNode node6 = new TreeNode(11);

root.left = node1;
root.right = node2;
node1.left = node3;
node1.right = node4;
node2.left = node5;
node2.right = node6;

BianliOfBinarryTree bianli=new BianliOfBinarryTree();
bianli.preOrder(root);
System.out.println("《《前序遍历-------");
bianli.inOrder(root);
System.out.println("《《中序遍历-------");
bianli.postOrder(root);
System.out.println("《《后序遍历-------");
bianli.preOrder2(root);
System.out.println("方法二：《《前序遍历-------");
bianli.inOrder2(root);
System.out.println("方法二：《《中序遍历-------");
// bianli.postOrder2(root);
System.out.println("方法二：《《后序遍历-------");
}

}