TheAlgorithms · siriak · Oct 20, 2021 · Oct 16, 2021 · Oct 16, 2021 · Oct 16, 2021
@@ -26,7 +26,7 @@ public class BSTRecursive {
 
   /** main function for tests */
   public static void main(String[] args) {
-    BSTIterative tree = new BSTIterative();
+    BSTRecursive tree = new BSTRecursive();
     tree.add(5);
     tree.add(10);
     tree.add(9);

@@ -0,0 +1,296 @@
+package DataStructures.Trees;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * <h1>Binary Search Tree (Recursive) Generic Type Implementation</h1>
+ *
+ * <p>
+ * A recursive implementation of generic type BST.
+ *
+ * Reference: https://en.wikipedia.org/wiki/Binary_search_tree
+ * </p>
+ *
+ * @author [Madhur Panwar](https://github.com/mdrpanwar)
+ */
+public class BSTRecursiveGeneric<T extends Comparable<T>> {
+  /** only data member is root of BST */
+  private Node<T> root;
+
+  /** Constructor use to initialize node as null */
+  public BSTRecursiveGeneric() {
+    root = null;
+  }
+
+  /** main function for testing */
+  public static void main(String[] args) {
+    System.out.println("Testing for integer data...");
+    // Integer
+    DataStructures.Trees.BSTRecursiveGeneric<Integer> integerTree = new DataStructures.Trees.BSTRecursiveGeneric<Integer>();
+
+    integerTree.add(5);
+    integerTree.add(10);
+    integerTree.add(9);
+    assert !integerTree.find(4) : "4 is not yet present in BST";
+    assert integerTree.find(10) : "10 should be present in BST";
+    integerTree.remove(9);
+    assert !integerTree.find(9) : "9 was just deleted from BST";
+    integerTree.remove(1);
+    assert !integerTree.find(1) : "Since 1 was not present so find deleting would do no change";
+    integerTree.add(20);
+    integerTree.add(70);
+    assert integerTree.find(70) : "70 was inserted but not found";
+    /*
+     Will print in following order
+     5 10 20 70
+    */
+    integerTree.inorder();
+    System.out.println();
+    System.out.println("Testing for string data...");
+    // String
+    DataStructures.Trees.BSTRecursiveGeneric<String> stringTree = new DataStructures.Trees.BSTRecursiveGeneric<String>();
+
+    stringTree.add("banana");
+    stringTree.add("pineapple");
+    stringTree.add("date");
+    assert !stringTree.find("girl") : "girl is not yet present in BST";
+    assert stringTree.find("pineapple") : "10 should be present in BST";
+    stringTree.remove("date");
+    assert !stringTree.find("date") : "date was just deleted from BST";
+    stringTree.remove("boy");
+    assert !stringTree.find("boy") : "Since boy was not present so deleting would do no change";
+    stringTree.add("india");
+    stringTree.add("hills");
+    assert stringTree.find("hills") : "hills was inserted but not found";
+    /*
+     Will print in following order
+     banana hills india pineapple
+    */
+    stringTree.inorder();
+
+  }
+
+  /**
+   * Recursive method to delete a data if present in BST.
+   *
+   * @param node the node under which to (recursively) search for data
+   * @param data the value to be deleted
+   * @return Node the updated value of root parameter after delete operation
+   */
+  private Node<T> delete(Node<T> node, T data) {
+    if (node == null) {
+      System.out.println("No such data present in BST.");
+    } else if (node.data.compareTo(data) > 0) {
+      node.left = delete(node.left, data);
+    } else if (node.data.compareTo(data) < 0) {
+      node.right = delete(node.right, data);
+    } else {
+      if (node.right == null && node.left == null) { // If it is leaf node
+        node = null;
+      } else if (node.left == null) { // If only right node is present
+        Node<T> temp = node.right;
+        node.right = null;
+        node = temp;
+      } else if (node.right == null) { // Only left node is present
+        Node<T> temp = node.left;
+        node.left = null;
+        node = temp;
+      } else { // both child are present
+        Node<T> temp = node.right;
+        // Find leftmost child of right subtree
+        while (temp.left != null) {
+          temp = temp.left;
+        }
+        node.data = temp.data;
+        node.right = delete(node.right, temp.data);
+      }
+    }
+    return node;
+  }
+
+  /**
+   * Recursive insertion of value in BST.
+   *
+   * @param node to check if the data can be inserted in current node or its subtree
+   * @param data the value to be inserted
+   * @return the modified value of the root parameter after insertion
+   */
+  private Node<T> insert(Node<T> node, T data) {
+    if (node == null) {
+      node = new Node<>(data);
+    } else if (node.data.compareTo(data) > 0) {
+      node.left = insert(node.left, data);
+    } else if (node.data.compareTo(data) < 0) {
+      node.right = insert(node.right, data);
+    }
+    return node;
+  }
+
+  /**
+   * Recursively print Preorder traversal of the BST
+   *
+   * @param node the root node
+   */
+  private void preOrder(Node<T> node) {
+    if (node == null) {
+      return;
+    }
+    System.out.print(node.data + " ");
+    if (node.left != null) {
+      preOrder(node.left);
+    }
+    if (node.right != null) {
+      preOrder(node.right);
+    }
+  }
+
+  /**
+   * Recursively print Postorder traversal of BST.
+   *
+   * @param node the root node
+   */
+  private void postOrder(Node<T> node) {
+    if (node == null) {
+      return;
+    }
+    if (node.left != null) {
+      postOrder(node.left);
+    }
+    if (node.right != null) {
+      postOrder(node.right);
+    }
+    System.out.print(node.data + " ");
+  }
+
+  /**
+   * Recursively print Inorder traversal of BST.
+   *
+   * @param node the root node
+   */
+  private void inOrder(Node<T> node) {
+    if (node == null) {
+      return;
+    }
+    if (node.left != null) {
+      inOrder(node.left);
+    }
+    System.out.print(node.data + " ");
+    if (node.right != null) {
+      inOrder(node.right);
+    }
+  }
+
+  /**
+   * Recursively traverse the tree using inorder traversal
+   * and keep adding elements to argument list.
+   *
+   * @param node the root node
+   * @param sortedList the list to add the srted elements into
+   */
+  private void inOrderSort(Node<T> node, List<T> sortedList) {
+    if (node == null) {
+      return;
+    }
+    if (node.left != null) {
+      inOrderSort(node.left, sortedList);
+    }
+    sortedList.add(node.data);
+    if (node.right != null) {
+      inOrderSort(node.right, sortedList);
+    }
+  }
+
+  /**
+   * Serach recursively if the given value is present in BST or not.
+   *
+   * @param node the node under which to check
+   * @param data the value to be checked
+   * @return boolean if data is present or not
+   */
+  private boolean search(Node<T> node, T data) {
+    if (node == null) {
+      return false;
+    } else if (node.data.compareTo(data) == 0) {
+      return true;
+    } else if (node.data.compareTo(data) > 0) {
+      return search(node.left, data);
+    } else {
+      return search(node.right, data);
+    }
+  }
+
+  /**
+   * add in BST. if the value is not already present it is inserted or else no change takes place.
+   *
+   * @param data the value to be inserted
+   */
+  public void add(T data) {
+    this.root = insert(this.root, data);
+  }
+
+  /**
+   * If data is present in BST delete it else do nothing.
+   *
+   * @param data the value to be removed
+   */
+  public void remove(T data) {
+    this.root = delete(this.root, data);
+  }
+
+  /** To call inorder traversal on tree */
+  public void inorder() {
+    System.out.println("Inorder traversal of this tree is:");
+    inOrder(this.root);
+    System.out.println(); // for next line
+  }
+
+  /** return a sorted list by traversing the tree elements using inorder traversal */
+  public List<T> inorderSort() {
+    List<T> sortedList = new ArrayList<>();
+    inOrderSort(this.root, sortedList);
+    return sortedList;
+  }
+
+  /** To call postorder traversal on tree */
+  public void postorder() {
+    System.out.println("Postorder traversal of this tree is:");
+    postOrder(this.root);
+    System.out.println(); // for next line
+  }
+
+  /** To call preorder traversal on tree. */
+  public void preorder() {
+    System.out.println("Preorder traversal of this tree is:");
+    preOrder(this.root);
+    System.out.println(); // for next line
+  }
+
+  /**
+   * To check if given value is present in tree or not.
+   *
+   * @param data the data to be found for
+   */
+  public boolean find(T data) {
+    if (search(this.root, data)) {
+      System.out.println(data + " is present in given BST.");
+      return true;
+    }
+    System.out.println(data + " not found.");
+    return false;
+  }
+
+  /** The generic Node class used for building binary search tree */
+  private static class Node<T> {
+    T data;
+    Node<T> left;
+    Node<T> right;
+
+    /** Constructor with data as parameter */
+    Node(T d) {
+      data = d;
+      left = null;
+      right = null;
+    }
+  }
+}