1 package com.basic.bt;
2
3 import java.util.ArrayList;
4 import java.util.Stack;
5
6 /**
7 * Created by mac on 2017/1/19.
8 */
9 public class PreOrderBT {
10
11 public ArrayList<Integer> result = new ArrayList<>();
12 public ArrayList<Integer> pre = new ArrayList<>();
13
15 public void preOrder(TreeNode root) {
16 if(root == null) {
17 return;
18 }
19 //访问跟 -> 左孩子 -> 右孩子
20 result.add(root.val);
21 preOrder(root.left);
22 preOrder(root.right);
23 }
24
25 // no recursion
26 public void preOrderTraversal(TreeNode root)
27 {
28 if(root == null) {
29 return;
30 }
31 Stack<TreeNode> stack = new Stack<TreeNode>();
32 stack.push(root);
33 while(!stack.isEmpty()) {
34 TreeNode node = stack.pop();
35 pre.add(node.val);
36 if(node.right != null) {
37 stack.push(node.right);
38 }
39 if(node.left != null) {
40 stack.push(node.left);
41 }
42 }
43
44 }
45
46 public static void main(String[] args) {
47 PreOrderBT pre = new PreOrderBT();
48 TreeNode root = new TreeNode(0);
49 TreeNode node1 = new TreeNode(1);
50 TreeNode node2 = new TreeNode(2);
51 TreeNode node3 = new TreeNode(3);
52 TreeNode node4 = new TreeNode(4);
53
54 root.left = node1;
55 root.right = node2;
56 node1.left = node3;
57 node1.right =node4;
58 pre.preOrderTraversal(root);
59 for(int i = 0; i < pre.pre.size(); i++) {
60 System.out.println(pre.pre.get(i));
61 }
62 }
63
64 }
