1 class TreeNode{
2 char data;
3 TreeNode left;
4 TreeNode right;
5 static int leaf;
6 static boolean flag=true;
7 TreeNode (char c){
8 data = c;
9 }
10 TreeNode (TreeNode n){
11 data = n.data;
12 left = n.left;
13 right = n.right;
14 }
15
16 public static void visit(TreeNode n){
17 if(n == null)
18 System.out.print("");
19 else{
20 if(flag){
21 System.out.print(n.data);
22 flag = false;
23 }else{
24 System.out.print(" " + n.data);
25 }
26 }
27 if(n.left == null && n.right == null) {
28 leaf++;
29 }
30 }
31
32 public static void preOrder(TreeNode root){
33 if(root == null) return;
34 visit(root);
35 preOrder(root.left);
36 preOrder(root.right);
37 }
38
39 // public static void preOrder2(TreeNode root){
40 // if(root == null) return;
41 // Stack<TreeNode> stack = new Stack<TreeNode>();
42 // stack.add(root);
43 // while(!stack.isEmpty()){
44 // TreeNode top = stack.pop();
45 // visit(top);
46 // if(top.right != null) stack.add(top.right);
47 // if(top.left != null) stack.add(top.left);
48 // }
49 // }
50
51 public static void preOrder2(TreeNode root){
52 if(root == null) return;
53 Stack<TreeNode> stack = new Stack<TreeNode>();
54 while(!stack.isEmpty() || root != null){
55 if(root != null){
56 stack.push(root);
57 visit(root);
58 root = root.left;
59 }else{
60 root = stack.pop();
61 root = root.right;
62 }
63 }
64 }
65 public static void inOrder(TreeNode root){
66 if(root == null) return;
67 inOrder(root.left);
68 visit(root);
69 inOrder(root.right);
70 }
71
72 public static void inOrder2(TreeNode root){
73 if(root == null) return;
74 Stack<TreeNode> stack = new Stack<TreeNode>();
75 while(!stack.empty() || root != null){
76 if(root != null){
77 stack.push(root);
78 root = root.left;
79 }else{
80 //reached leftMost
81 root = stack.pop();
82 visit(root);
83 root = root.right;
84 }
85 }
86 }
87
88 public static void postOrder(TreeNode root){
89 if(root == null) return;
90 postOrder(root.left);
91 postOrder(root.right);
92 visit(root);
93 }
94
95 public static void levelOrder(TreeNode root){
96 if(root == null) return;
97 LinkedList<TreeNode> q = new LinkedList<TreeNode>();
98 q.add(root);
99 while(!q.isEmpty()){
100 TreeNode head = q.removeFirst();
101 visit(head);
102 if(head.left != null) q.add(head.left);
103 if(head.right != null) q.add(head.right);
104 }
105 }
106
107 public static void zigzagOrder(TreeNode root){
108 LinkedList<TreeNode> currentLevel = new LinkedList<TreeNode>();
109 int level = 0;
110 if(root != null)
111 currentLevel.add(root);
112 while(!currentLevel.isEmpty()){
113 LinkedList<TreeNode> nextLevel = new LinkedList<TreeNode>();
114 ArrayList<TreeNode> list = new ArrayList<TreeNode>();
115 for(TreeNode node : currentLevel){
116 list.add(node);
117 if(node.left != null)
118 nextLevel.add(node.left);
119 if(node.right != null)
120 nextLevel.add(node.right);
121 }
122 if(level%2 == 1)
123 Collections.reverse(list);
124 for(int i = 0; i < list.size(); i++)
125 visit(list.get(i));
126 currentLevel = nextLevel;
127 level++;
128 }
129
130 }
131
132 }
