Create PreorderTraversalOfBinaryTree.java

code/hacktober/PreorderTraversalOfBinaryTree.java

@@ -0,0 +1,78 @@
+/*
+ * Java Program to traverse a binary tree using PreOrder traversal. 
+ * In PreOrder the node value is printed first, followed by visit
+ * to left and right subtree. 
+ * input:
+ *     A
+ *    / \
+ *   B   E
+ *  / \   \
+ * C   D   F
+ * 
+ * output: A B C D E F 
+ */
+
+public class Main {
+
+  public static void main(String[] args) throws Exception {
+
+    // construct the binary tree given in question
+    BinaryTree bt = new BinaryTree();
+    BinaryTree.TreeNode root = new BinaryTree.TreeNode("A");
+    bt.root = root;
+    bt.root.left = new BinaryTree.TreeNode("B");
+    bt.root.left.left = new BinaryTree.TreeNode("C");
+
+    bt.root.left.right = new BinaryTree.TreeNode("D");
+    bt.root.right = new BinaryTree.TreeNode("E");
+    bt.root.right.right = new BinaryTree.TreeNode("F");
+
+    // visitng nodes in preOrder traversal
+    System.out.println("printing nodes of a binary tree in preOrder 
+                        using recursion");
+    bt.preOrder();
+
+  }
+
+}
+
+class BinaryTree {
+  static class TreeNode {
+    String data;
+    TreeNode left, right;
+
+    TreeNode(String value) {
+      this.data = value;
+      left = right = null;
+    }
+
+    boolean isLeaf() {
+      return left == null ? right == null : false;
+    }
+
+  }
+
+  // root of binary tree
+  TreeNode root;
+
+  /**
+   * Java method to print tree nodes in PreOrder traversal
+   */
+  public void preOrder() {
+    preOrder(root);
+  }
+
+  /**
+   * traverse the binary tree in PreOrder
+   * @param node - starting node, root
+   */
+  private void preOrder(TreeNode node) {
+    if (node == null) {
+      return;
+    }
+    System.out.printf("%s ", node.data);
+    preOrder(node.left);
+    preOrder(node.right);
+  }
+
+}