add tree code

.gitignore

@@ -1,2 +1,2 @@
 .idea
-*.iml
+*.iml

pom.xml

@@ -4,7 +4,7 @@
          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
 
-    <groupId>bit.edu.bitcarmanlee</groupId>
+    <groupId>edu.bit.bitcarmanlee</groupId>
     <artifactId>easy-algorithm-interview</artifactId>
     <version>1.0-SNAPSHOT</version>
 

src/main/java/edu/bit/carmanlee/datastruct/tree/Traverse.java

@@ -0,0 +1,95 @@
+package edu.bit.carmanlee.datastruct.tree;
+
+import java.util.Stack;
+
+public class Traverse {
+
+    public static void preorder(TreeNode root) {
+        if (root == null) return;
+        System.out.print(root.data + " ");
+        preorder(root.left);
+        preorder(root.right);
+    }
+
+    public static void preordernorecursive(TreeNode root) {
+        if (root == null) return;
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(root);
+        while (!stack.isEmpty()) {
+            TreeNode tmp = stack.pop();
+            System.out.print(tmp.data + " ");
+            if (tmp.right != null) stack.push(tmp.right);
+            if (tmp.left != null) stack.push(tmp.left);
+        }
+    }
+
+    public static void inorder(TreeNode root) {
+        if (root == null) return;
+        inorder(root.left);
+        System.out.print(root.data + " ");
+        inorder(root.right);
+    }
+
+    public static void inorernorecursive(TreeNode root) {
+        if (root == null) return;
+        Stack<TreeNode> stack = new Stack<>();
+        while (!stack.isEmpty() || root != null) {
+            while (root != null) {
+                stack.push(root);
+                root = root.left;
+            }
+            if (!stack.isEmpty()) {
+                root = stack.pop();
+                System.out.print(root.data + " ");
+                root = root.right;
+            }
+        }
+    }
+
+    public static void postorder(TreeNode root) {
+        if (root == null) return;
+        postorder(root.left);
+        postorder(root.right);
+        System.out.print(root.data + " ");
+    }
+
+    public static void postordernorecursive(TreeNode root) {
+        if (root == null) return;
+        Stack<TreeNode> stack = new Stack<>();
+        TreeNode pre = root, cur = root;
+        while (cur != null) {
+            stack.push(cur);
+            cur = cur.left;
+        }
+
+        while (! stack.isEmpty()) {
+            cur = stack.pop();
+            if (cur.right != null && cur.right != pre) {
+                stack.push(cur);
+                cur = cur.right;
+                while (cur != null) {
+                    stack.push(cur);
+                    cur = cur.left;
+                }
+            } else {
+                System.out.print(cur.data + " ");
+                pre = cur;
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        TreeNode root = TreeNodeInit.init();
+        preorder(root);
+        System.out.println();
+        preordernorecursive(root);
+        System.out.println();
+        inorder(root);
+        System.out.println();
+        inorernorecursive(root);
+        System.out.println();
+        postorder(root);
+        System.out.println();
+        postordernorecursive(root);
+    }
+}

src/main/java/edu/bit/carmanlee/datastruct/tree/TreeNode.java

@@ -0,0 +1,13 @@
+package edu.bit.carmanlee.datastruct.tree;
+
+public class TreeNode {
+
+    int data;
+    TreeNode left, right;
+
+    public TreeNode(int data) {
+        this.data = data;
+    }
+
+
+}

src/main/java/edu/bit/carmanlee/datastruct/tree/TreeNodeInit.java

@@ -0,0 +1,32 @@
+package edu.bit.carmanlee.datastruct.tree;
+
+public class TreeNodeInit {
+
+
+    /*
+           1
+        2      3
+     4    5  6   7
+       8
+ */
+    public static TreeNode init() {
+        TreeNode t1 = new TreeNode(1);
+        TreeNode t2 = new TreeNode(2);
+        TreeNode t3 = new TreeNode(3);
+        TreeNode t4 = new TreeNode(4);
+        TreeNode t5 = new TreeNode(5);
+        TreeNode t6 = new TreeNode(6);
+        TreeNode t7 = new TreeNode(7);
+        TreeNode t8 = new TreeNode(8);
+        t1.left = t2;
+        t1.right = t3;
+        t2.left = t4;
+        t2.right = t5;
+        t3.left = t6;
+        t3.right = t7;
+        t4.right = t8;
+        return t1;
+
+    }
+
+}