Added Tree Data Structure folder

Added Inorder Tree Traversal in this change.

Author: Gaurav Sonwani

Tree/BinaryTree.java

@@ -0,0 +1,98 @@
+package Tree;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Stack;
+
+public class BinaryTree {
+    BinaryTreeNode root;
+
+    BinaryTree() {
+    }
+
+    BinaryTree(int d) {
+        root = new BinaryTreeNode(d);
+    }
+
+    /* Recursive approach of inOrder Traversal of Tree
+     * Time Complexity: O(n)
+     * Space Complexity: O(n) (implicit)
+     */
+    public void inOrder(BinaryTreeNode root) {
+        if (root == null) return;
+        inOrder(root.left);
+        System.out.print(root.data + " ");
+        inOrder(root.right);
+    }
+
+    /* Iterative  approach of inOrder Traversal of Tree
+     * Time Complexity: O(n)
+     * Space Complexity: O(n) (explicit)
+     */
+    public void inOrderWithoutRecursion(BinaryTreeNode root) {
+        if (root == null) return;
+        Stack<BinaryTreeNode> stack = new Stack<BinaryTreeNode>();
+
+        while (root != null) {
+            stack.push(root);
+            root = root.left;
+        }
+        while (!stack.empty()) {
+            BinaryTreeNode temp = stack.pop();
+            System.out.print(temp.data + " ");
+            if (temp.right != null)
+                root = temp.right;
+            while (root != null) {
+                stack.push(root);
+                root = root.left;
+            }
+        }
+    }
+
+    /* inOrder Traversal of Tree with using any extra space, Morris Traversal
+     * Time Complexity: O(n)
+     * Space Complexity: O(1)
+     */
+    public void inOrderMorrisTraversal(BinaryTreeNode root) {
+        while (root != null) {
+            if (root.left == null) {
+                System.out.print(root.data + " ");
+                root = root.right;
+            } else {
+                BinaryTreeNode prev = root.left;
+                while (prev.right != null && prev.right != root)
+                    prev = prev.right;
+                if (prev.right == null) {
+                    prev.right = root;
+                    root = root.left;
+                } else {
+                    prev.right = null;
+                    System.out.print(root.data + " ");
+                    root = root.right;
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        BinaryTree binaryTree = new BinaryTree();
+        binaryTree.root = new BinaryTreeNode(1);
+        binaryTree.root.left = new BinaryTreeNode(2);
+        binaryTree.root.right = new BinaryTreeNode(3);
+        binaryTree.root.left.left = new BinaryTreeNode(4);
+        binaryTree.root.left.right = new BinaryTreeNode(5);
+        binaryTree.root.right.right = new BinaryTreeNode(6);
+        binaryTree.root.left.left.right = new BinaryTreeNode(7);
+        binaryTree.root.left.right.left = new BinaryTreeNode(8);
+        binaryTree.root.right.right.left = new BinaryTreeNode(9);
+
+        System.out.println("\nInOrder");
+        binaryTree.inOrder(binaryTree.root);
+
+        System.out.println("\nInOrderWithoutRecurion");
+        binaryTree.inOrderWithoutRecursion(binaryTree.root);
+        System.out.println("\nInOrderMorrisTraversal");
+        binaryTree.inOrderMorrisTraversal(binaryTree.root);
+
+    }
+}

Tree/BinaryTreeNode.java

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+package Tree;
+
+public class BinaryTreeNode {
+    int data;
+    BinaryTreeNode left;
+    BinaryTreeNode right;
+    BinaryTreeNode(int data) {
+        this.data = data;
+        left = null;
+        right = null;
+    }
+}