树的前序、中序、后序遍历的JAVA实现

【注】后续实现第二种方法暂时未解出

  1 package com.exe4.offer;
  2
  3 import java.util.Stack;
  4
  5 /**
  6  * 前序、中序、后序遍历方法
  7  * @author WGS
  8  *
  9  */
 10 public class BianliOfBinarryTree {
 11      public static class TreeNode {
 12             int val = 0;
 13             TreeNode left = null;
 14             TreeNode right = null;
 15
 16             public TreeNode(int val) {
 17                 this.val = val;
 18
 19             }
 20      }
 21     /**
 22      * 方法一：大话数据结构中简便方法，可实现操作。
 23      * @param args
 24      */
 25
 26     public void preOrder(TreeNode node){
 27         if(node==null) return;
 28         System.out.print(node.val+"  ");
 29         preOrder(node.left);
 30         preOrder(node.right);
 31     }
 32     public void inOrder(TreeNode node){
 33         if(node==null) return;
 34         inOrder(node.left);
 35         System.out.print(node.val+"  ");
 36         inOrder(node.right);
 37     }
 38     public void postOrder(TreeNode node){
 39         if(node==null) return;
 40         postOrder(node.left);
 41         postOrder(node.right);
 42         System.out.print(node.val+"  ");
 43     }
 44     /**
 45      * 方法二：剑指offer中的方法：加入栈操作
 46      * @param args
 47      */
 48     public void preOrder2(TreeNode node){
 49         Stack<TreeNode> stack=new Stack<TreeNode>();
 50
 51         while(node!=null || !stack.empty()){
 52             //先遍历左子树
 53             while(node!=null){
 54                 System.out.print(node.val+"  ");
 55                 stack.push(node);
 56                 node=node.left;//左子树遍历结束后，node==null,跳出此循环
 57             }
 58             //左子树遍历结束，继续遍历右子树
 59             if(!stack.isEmpty()){
 60                 node=stack.pop();//一直返回，直到根节点处，node==null，即stack==isEmpty()
 61                 node=node.right;
 62             }
 63         }
 64     }
 65     public void inOrder2(TreeNode node){
 66         Stack<TreeNode> stack=new Stack<TreeNode>();
 67         while(node!=null || !stack.isEmpty()){
 68
 69             while(node!=null){
 70                 stack.push(node);//8 6  5
 71                 node=node.left;    //6  5  null
 72             }
 73
 74             if(!stack.isEmpty()){
 75                 node=stack.pop();//5  6
 76                 System.out.print(node.val+"  ");//5  6
 77                 node=node.right;//null
 78             }
 79         }
 80     }
 81     //后序遍历暂时还不会
 82     /*public void postOrder2(TreeNode node){
 83         Stack<TreeNode> stack=new Stack<TreeNode>();
 84         while(node!=null ||  !stack.isEmpty()){
 85             while(node!=null){
 86                 stack.push(node);//8 6 5  7
 87                 node=node.left;//6 5 null null
 88             }
 89             if(!stack.isEmpty()){
 90                 node=stack.pop();//5 6     7
 91                 node=node.right;//null 7  null
 92
 93             }
 94
 95         }
 96     }*/
 97
 98     public static void main(String[] args) {
 99             TreeNode root = new TreeNode(8);
100             TreeNode node1 = new TreeNode(6);
101             TreeNode node2 = new TreeNode(10);
102             TreeNode node3 = new TreeNode(5);
103             TreeNode node4 = new TreeNode(7);
104             TreeNode node5 = new TreeNode(9);
105             TreeNode node6 = new TreeNode(11);
106
107             root.left = node1;
108             root.right = node2;
109             node1.left = node3;
110             node1.right = node4;
111             node2.left = node5;
112             node2.right = node6;
113
114             BianliOfBinarryTree bianli=new BianliOfBinarryTree();
115             bianli.preOrder(root);
116             System.out.println("《《前序遍历-------");
117             bianli.inOrder(root);
118             System.out.println("《《中序遍历-------");
119             bianli.postOrder(root);
120             System.out.println("《《后序遍历-------");
121             bianli.preOrder2(root);
122             System.out.println("方法二：《《前序遍历-------");
123             bianli.inOrder2(root);
124             System.out.println("方法二：《《中序遍历-------");
125            // bianli.postOrder2(root);
126             System.out.println("方法二：《《后序遍历-------");
127     }
128
129 }