DS: Binary Search Tree added Closes #1420

DataStructures/Trees/BSTIterative.java

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+/**
+ *
+ *
+ * <h1>Binary Search Tree (Iterative)</h1>
+ *
+ * An implementation of BST iteratively. 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.
+ *
+ * @author [Lakhan Nad](https://github.com/Lakhan-Nad)
+ */
+import java.util.Stack;
+
+public class BSTIterative {
+  /** Reference for the node of BST. */
+  private Node root;
+
+  /** Default Constructor Initializes the root of BST with null. */
+  BSTIterative() {
+    root = null;
+  }
+
+  /**
+   * A method to insert a new value in BST. If the given value is already present in BST the
+   * insertion is ignored.
+   *
+   * @param data the value to be inserted
+   */
+  public void add(int data) {
+    Node parent = null;
+    Node temp = this.root;
+    int rightOrLeft = -1;
+    /* Finds the proper place this node can
+     * be placed in according to rules of BST.
+     */
+    while (temp != null) {
+      if (temp.data > data) {
+        parent = temp;
+        temp = parent.left;
+        rightOrLeft = 0;
+      } else if (temp.data < data) {
+        parent = temp;
+        temp = parent.right;
+        rightOrLeft = 1;
+      } else {
+        System.out.println(data + " is already present in BST.");
+        return; // if data already present we ignore insertion
+      }
+    }
+    /* Creates a newnode with the value passed
+     * Since this data doesn't already exists
+     */
+    Node newnode = new Node(data);
+    /* If the parent node is null
+     * then the insertion is to be done in
+     * root itself.
+     */
+    if (parent == null) {
+      this.root = newnode;
+    } else {
+      /* Check if insertion is to be made in
+       * left or right subtree.
+       */
+      if (rightOrLeft == 0) {
+        parent.left = newnode;
+      } else {
+        parent.right = newnode;
+      }
+    }
+  }
+
+  /**
+   * A method to delete the node in BST. If node is present it will be deleted
+   *
+   * @param data the value that needs to be deleted
+   */
+  public void remove(int data) {
+    Node parent = null;
+    Node temp = this.root;
+    int rightOrLeft = -1;
+    /* Find the parent of the node and node itself
+     * That is to be deleted.
+     * parent variable store parent
+     * temp stores node itself.
+     * rightOrLeft use to keep track weather child
+     * is left or right subtree
+     */
+    while (temp != null) {
+      if (temp.data == data) {
+        break;
+      } else if (temp.data > data) {
+        parent = temp;
+        temp = parent.left;
+        rightOrLeft = 0;
+      } else {
+        parent = temp;
+        temp = parent.right;
+        rightOrLeft = 1;
+      }
+    }
+    /* If temp is null than node with given value is not
+     * present in our tree.
+     */
+    if (temp != null) {
+      Node replacement; // used to store the new values for replacing nodes
+      if (temp.right == null && temp.left == null) { // Leaf node Case
+        replacement = null;
+      } else if (temp.right == null) { // Node with only right child
+        replacement = temp.left;
+        temp.left = null;
+      } else if (temp.left == null) { // Node with only left child
+        replacement = temp.right;
+        temp.right = null;
+      } else {
+        /* If both left and right child are present
+         * we replace this nodes data with
+         * leftmost node's data in its right subtree
+         * to maintain the balance of BST.
+         * And then delete that node
+         */
+        if (temp.right.left == null) {
+          temp.data = temp.right.data;
+          replacement = temp;
+          temp.right = temp.right.right;
+        } else {
+          Node parent2 = temp.right;
+          Node child = temp.right.left;
+          while (child.left != null) {
+            parent2 = child;
+            child = parent2.left;
+          }
+          temp.data = child.data;
+          parent2.left = child.right;
+          replacement = temp;
+        }
+      }
+      /* Change references of parent after
+       * deleting the child.
+       */
+      if (parent == null) {
+        this.root = replacement;
+      } else {
+        if (rightOrLeft == 0) {
+          parent.left = replacement;
+        } else {
+          parent.right = replacement;
+        }
+      }
+    }
+  }
+
+  /** A method for inorder traversal of BST. */
+  public void inorder() {
+    if (this.root == null) {
+      System.out.println("This BST is empty.");
+      return;
+    }
+    System.out.println("Inorder traversal of this tree is:");
+    Stack<Node> st = new Stack<Node>();
+    Node cur = this.root;
+    while (cur != null || !st.empty()) {
+      while (cur != null) {
+        st.push(cur);
+        cur = cur.left;
+      }
+      cur = st.pop();
+      System.out.print(cur.data + " ");
+      cur = cur.right;
+    }
+    System.out.println(); // for next line
+  }
+
+  /** A method used to print postorder traversal of BST. */
+  public void postorder() {
+    if (this.root == null) {
+      System.out.println("This BST is empty.");
+      return;
+    }
+    System.out.println("Postorder traversal of this tree is:");
+    Stack<Node> st = new Stack<Node>();
+    Node cur = this.root, temp2;
+    while (cur != null || !st.empty()) {
+      if (cur != null) {
+        st.push(cur);
+        cur = cur.left;
+      } else {
+        temp2 = st.peek();
+        if (temp2.right != null) {
+          cur = temp2.right;
+        } else {
+          st.pop();
+          while (!st.empty() && st.peek().right == temp2) {
+            System.out.print(temp2.data + " ");
+            temp2 = st.pop();
+          }
+          System.out.print(temp2.data + " ");
+        }
+      }
+    }
+    System.out.println(); // for next line
+  }
+
+  /** Method used to display preorder traversal of BST. */
+  public void preorder() {
+    if (this.root == null) {
+      System.out.println("This BST is empty.");
+      return;
+    }
+    System.out.println("Preorder traversal of this tree is:");
+    Stack<Node> st = new Stack<Node>();
+    st.push(this.root);
+    Node temp;
+    while (!st.empty()) {
+      temp = st.pop();
+      System.out.print(temp.data + " ");
+      if (temp.right != null) {
+        st.push(temp.right);
+      }
+      if (temp.left != null) {
+        st.push(temp.left);
+      }
+    }
+    System.out.println(); // for next line
+  }
+
+  /**
+   * A method to check if given data exists in out Binary Search Tree.
+   *
+   * @param data the value that needs to be searched for
+   * @return boolean representing if the value was find
+   */
+  public boolean find(int data) {
+    Node temp = this.root;
+    /* Check if node exists
+     */
+    while (temp != null) {
+      if (temp.data > data) {
+        temp = temp.left;
+      } else if (temp.data < data) {
+        temp = temp.right;
+      } else {
+        /* If found return true
+         */
+        System.out.println(data + " is present in the BST.");
+        return true;
+      }
+    }
+    System.out.println(data + " not found.");
+    return false;
+  }
+
+  /** The Node class used for building binary search tree */
+  private class Node {
+    int data;
+    Node left;
+    Node right;
+
+    /** Constructor with data as parameter */
+    Node(int d) {
+      data = d;
+      left = null;
+      right = null;
+    }
+  }
+}

DataStructures/Trees/BSTRecursive.java

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+/**
+ *
+ *
+ * <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;
+  }
+
+  /**
+   * Recursive method to delete a data if present in BST.
+   *
+   * @param root 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 root, int data) {
+    if (root == null) {
+      System.out.println("No such data present in BST.");
+    } else if (root.data > data) {
+      root.left = delete(root.left, data);
+    } else if (root.data < data) {
+      root.right = delete(root.right, data);
+    } else {
+      if (root.right == null && root.left == null) { // If it is leaf node
+        root = null;
+      } else if (root.left == null) { // If only right node is present
+        Node temp = root.right;
+        root.right = null;
+        root = temp;
+      } else if (root.right == null) { // Only left node is present
+        Node temp = root.left;
+        root.left = null;
+        root = temp;
+      } else { // both child are present
+        Node temp = root.right;
+        // Find leftmost child of right subtree
+        while (temp.left != null) {
+          temp = temp.left;
+        }
+        root.data = temp.data;
+        root.right = delete(root.right, temp.data);
+      }
+    }
+    return root;
+  }
+
+  /**
+   * Recursive insertion of value in BST.
+   *
+   * @param root 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 root, int data) {
+    if (root == null) {
+      root = new Node(data);
+    } else if (root.data > data) {
+      root.left = insert(root.left, data);
+    } else if (root.data < data) {
+      root.right = insert(root.right, data);
+    }
+    return root;
+  }
+
+  /**
+   * Recursively print Preorder traversal of the BST
+   *
+   * @param root
+   */
+  private void preOrder(Node root) {
+    if (root == null) {
+      return;
+    }
+    System.out.print(root.data + " ");
+    if (root.left != null) {
+      preOrder(root.left);
+    }
+    if (root.right != null) {
+      preOrder(root.right);
+    }
+  }
+
+  /**
+   * Recursively print Postorder travesal of BST.
+   *
+   * @param root
+   */
+  private void postOrder(Node root) {
+    if (root == null) {
+      return;
+    }
+    if (root.left != null) {
+      postOrder(root.left);
+    }
+    if (root.right != null) {
+      postOrder(root.right);
+    }
+    System.out.print(root.data + " ");
+  }
+
+  /**
+   * Recursively print Inorder traversal of BST.
+   *
+   * @param root
+   */
+  private void inOrder(Node root) {
+    if (root == null) {
+      return;
+    }
+    if (root.left != null) {
+      inOrder(root.left);
+    }
+    System.out.print(root.data + " ");
+    if (root.right != null) {
+      inOrder(root.right);
+    }
+  }
+
+  /**
+   * Serach recursively if the given value is present in BST or not.
+   *
+   * @param root the current node to check
+   * @param data the value to be checked
+   * @return boolean if data is present or not
+   */
+  private boolean search(Node root, int data) {
+    if (root == null) {
+      return false;
+    } else if (root.data == data) {
+      return true;
+    } else if (root.data > data) {
+      return search(root.left, data);
+    } else {
+      return search(root.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
+   */
+  public void 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 class Node {
+    int data;
+    Node left;
+    Node right;
+
+    /** Constructor with data as parameter */
+    Node(int d) {
+      data = d;
+      left = null;
+      right = null;
+    }
+  }
+}