JavaAlgorithms/DataStructures/Trees/BSTRecursive.java

/**
 *
 *
 * <h1>Binary Search Tree (Recursive)</h1>
 *
 * An implementation of BST recursively. In recursive implementation the checks are down the tree
 * First root is checked if not found then its childs are checked Binary Search Tree is a binary
 * tree which satisfies three properties: left child is less than root node, right child is grater
 * than root node, both left and right childs must themselves be a BST.
 *
 * <p>I have made public functions as methods and to actually implement recursive approach I have
 * used private methods
 *
 * @author [Lakhan Nad](https://github.com/Lakhan-Nad)
 */
public class BSTRecursive {
  /** only data member is root of BST */
  private Node root;

  /** Constructor use to initialize node as null */
  BSTRecursive() {
    root = null;
  }

  /** main function for tests */
  public static void main(String[] args) {
    BSTIterative tree = new BSTIterative();
    tree.add(5);
    tree.add(10);
    tree.add(9);
    assert !tree.find(4) : "4 is not yet present in BST";
    assert tree.find(10) : "10 should be present in BST";
    tree.remove(9);
    assert !tree.find(9) : "9 was just deleted from BST";
    tree.remove(1);
    assert !tree.find(1) : "Since 1 was not present so find deleting would do no change";
    tree.add(20);
    tree.add(70);
    assert tree.find(70) : "70 was inserted but not found";
    /*
     Will print in following order
     5 10 20 70
    */
    tree.inorder();
  }

  /**
   * Recursive method to delete a data if present in BST.
   *
   * @param node the current node to search for data
   * @param data the value to be deleted
   * @return Node the updated value of root parameter after delete operation
   */
  private Node delete(Node node, int data) {
    if (node == null) {
      System.out.println("No such data present in BST.");
    } else if (node.data > data) {
      node.left = delete(node.left, data);
    } else if (node.data < data) {
      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 temp = node.right;
        node.right = null;
        node = temp;
      } else if (node.right == null) { // Only left node is present
        Node temp = node.left;
        node.left = null;
        node = temp;
      } else { // both child are present
        Node 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 insert(Node node, int data) {
    if (node == null) {
      node = new Node(data);
    } else if (node.data > data) {
      node.left = insert(node.left, data);
    } else if (node.data < data) {
      node.right = insert(node.right, data);
    }
    return node;
  }

  /**
   * Recursively print Preorder traversal of the BST
   *
   * @param node the root node
   */
  private void preOrder(Node 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 travesal of BST.
   *
   * @param node the root node
   */
  private void postOrder(Node 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 node) {
    if (node == null) {
      return;
    }
    if (node.left != null) {
      inOrder(node.left);
    }
    System.out.print(node.data + " ");
    if (node.right != null) {
      inOrder(node.right);
    }
  }

  /**
   * Serach recursively if the given value is present in BST or not.
   *
   * @param node the current node to check
   * @param data the value to be checked
   * @return boolean if data is present or not
   */
  private boolean search(Node node, int data) {
    if (node == null) {
      return false;
    } else if (node.data == data) {
      return true;
    } else if (node.data > data) {
      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(int 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(int 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
  }

  /** 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 li
  }

  /** 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 li
  }

  /**
   * To check if given value is present in tree or not.
   *
   * @param data the data to be found for
   */
  public boolean find(int 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 Node class used for building binary search tree */
  private static class Node {
    int data;
    Node left;
    Node right;

    /** Constructor with data as parameter */
    Node(int d) {
      data = d;
      left = null;
      right = null;
    }
  }
}