Binary Search Tree Insertion Method in Java Explained

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Question :

Binary Search Tree Insertion Method in Java, explain it and give me a code example

Réponse :

A Binary Search Tree (BST) is a data structure that maintains sorted order of elements, allowing for efficient insertion, deletion, and lookup operations. In a BST, each node has at most two children, and for any given node:

  • The left child's value is less than the node's value.
  • The right child's value is greater than the node's value.

Insertion Method

The insertion method for a BST involves the following steps:

  1. Start at the root: If the tree is empty, the new node becomes the root.
  2. Compare the new value with the current node's value:
    • If the new value is less than the current node's value, move to the left child.
    • If the new value is greater than the current node's value, move to the right child.
  3. Repeat the comparison until you find an empty spot (null) where the new node can be inserted.
  4. Insert the new node at the found position.

Code Example

Here is a simple implementation of a Binary Search Tree in Java, including the insertion method:

class TreeNode {
    int value;
    TreeNode left;
    TreeNode right;

    TreeNode(int value) {
        this.value = value;
        this.left = null;
        this.right = null;
    }
}

class BinarySearchTree {
    private TreeNode root;

    public BinarySearchTree() {
        this.root = null;
    }

    // Public method to insert a value
    public void insert(int value) {
        root = insertRec(root, value);
    }

    // Recursive method to insert a value
    private TreeNode insertRec(TreeNode node, int value) {
        // If the current node is null, create a new node
        if (node == null) {
            return new TreeNode(value);
        }

        // Otherwise, recur down the tree
        if (value < node.value) {
            node.left = insertRec(node.left, value);
        } else if (value > node.value) {
            node.right = insertRec(node.right, value);
        }
        // Return the unchanged node pointer
        return node;
    }

    // In-order traversal to display the tree
    public void inorder() {
        inorderRec(root);
    }

    private void inorderRec(TreeNode node) {
        if (node != null) {
            inorderRec(node.left);
            System.out.print(node.value + " ");
            inorderRec(node.right);
        }
    }

    public static void main(String[] args) {
        BinarySearchTree bst = new BinarySearchTree();
        bst.insert(50);
        bst.insert(30);
        bst.insert(20);
        bst.insert(40);
        bst.insert(70);
        bst.insert(60);
        bst.insert(80);

        System.out.println("In-order traversal of the BST:");
        bst.inorder(); // Output: 20 30 40 50 60 70 80
    }
}

Explanation of the Code

  1. TreeNode Class: Represents a node in the BST. It contains an integer value and pointers to the left and right children.
  2. BinarySearchTree Class: Contains methods for inserting values and performing an in-order traversal.
    • The insert method is a public method that starts the insertion process.
    • The insertRec method is a private recursive method that handles the actual insertion logic.
  3. In-order Traversal: The inorder method prints the values of the BST in sorted order by recursively visiting the left child, the current node, and then the right child.
  4. Main Method: Demonstrates how to create a BST, insert values, and print them in sorted order.

This implementation provides a basic structure for a Binary Search Tree and can be expanded with additional features such as deletion, searching, and balancing.

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