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Data Structures for Coding Interviews in C++

Deletion in Binary Search Tree (Implementation)

Explore how to implement deletion operations in binary search trees using C++. Understand and handle each scenario from deleting empty trees, leaf nodes, nodes with one or two children, and apply these concepts with an efficient code example.

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Introduction

Let’s implement the delete function for BSTs. We’ll build upon the code as we cater for each case.

1. Deleting an empty tree

Let’s start with a skeleton function definition and cater for the first case. We return false if the root is NULL.

C++
Delete(Node* currentNode,int value) {
    if(root==NULL)
        return false;
}

2. val not found

We search for the tree for the data given, and if it’s not found, i.e., currentNode is NULL, we return false.

C++
bool Delete(Node* currentNode,int value) {
        if(root==NULL){
            return false;
        }
        Node* parent; //To Store parent of currentNode
        while(currentNode!=NULL && (currentNode->value != value)) {
            parent=currentNode;
            if (currentNode->value > value)
                currentNode=currentNode->leftChild;
            else
                currentNode=currentNode->rightChild;
        }
        if(currentNode==NULL)
            return false;
}
C++
#include "BST.h"
Node::Node() {
  value = 0;
  leftChild = NULL;
  rightChild = NULL;
}
Node::Node(int val) {
  value = val;
  leftChild = NULL;
  rightChild = NULL;
}
BinarySearchTree::BinarySearchTree() {
  root = NULL;
}
BinarySearchTree::BinarySearchTree(int rootValue) {
  root = new Node(rootValue);
}
Node * BinarySearchTree::getRoot() {
  return root;
}
Node * BinarySearchTree::insert(Node * currentNode, int val) {
  if (currentNode == NULL) {
    return new Node(val);
  }
  else if (currentNode -> value > val) {
    currentNode -> leftChild = insert(currentNode -> leftChild, val);
  } 
  else {
    currentNode -> rightChild = insert(currentNode -> rightChild, val);
  }
  return currentNode;
}
void BinarySearchTree::insertBST(int value) {
  if (getRoot() == NULL) {
    root = new Node(value);
    return;
  }
  insert(this -> getRoot(), value);
}
bool BinarySearchTree::Delete(Node * currentNode, int value) {
  if (root == NULL) {
    return false;
  }
  Node * parent; //To Store parent of currentNode
  while (currentNode != NULL && (currentNode -> value != value)) {
    parent = currentNode;
    if (currentNode -> value > value)
      currentNode = currentNode -> leftChild;
    else
      currentNode = currentNode -> rightChild;
  }
  if (currentNode == NULL){
    return false;
  }
  return false;
}
bool BinarySearchTree::deleteBST(int value) {
  return Delete(root, value);
}
void BinarySearchTree::inOrderPrint(Node * currentNode) {
  if (currentNode != NULL) {
    inOrderPrint(currentNode -> leftChild);
    cout << currentNode -> value << endl;
    inOrderPrint(currentNode -> rightChild);
  }
}

3. Deleting a Leaf Node

We first search for the value given to ...