BSTDeletion_CPP.cpp

/* Deleting a node from Binary search tree */
#include<iostream>
using namespace std;
struct Node {
	int data;
	struct Node *left;
	struct Node *right;
};
//Function to find minimum in a tree. 
Node* FindMin(Node* root)
{
	while(root->left != NULL) root = root->left;
	return root;
}

// Function to search a delete a value from tree.
struct Node* Delete(struct Node *root, int data) {
	if(root == NULL) return root; 
	else if(data < root->data) root->left = Delete(root->left,data);
	else if (data > root->data) root->right = Delete(root->right,data);
	// Wohoo... I found you, Get ready to be deleted	
	else {
		// Case 1:  No child
		if(root->left == NULL && root->right == NULL) { 
			delete root;
			root = NULL;
		}
		//Case 2: One child 
		else if(root->left == NULL) {
			struct Node *temp = root;
			root = root->right;
			delete temp;
		}
		else if(root->right == NULL) {
			struct Node *temp = root;
			root = root->left;
			delete temp;
		}
		// case 3: 2 children
		else { 
			struct Node *temp = FindMin(root->right);
			root->data = temp->data;
			root->right = Delete(root->right,temp->data);
		}
	}
	return root;
}
 
//Function to visit nodes in Inorder
void Inorder(Node *root) {
	if(root == NULL) return;
 
	Inorder(root->left);       //Visit left subtree
	printf("%d ",root->data);  //Print data
	Inorder(root->right);      // Visit right subtree
}
 
// Function to Insert Node in a Binary Search Tree
Node* Insert(Node *root,char data) {
	if(root == NULL) {
		root = new Node();
		root->data = data;
		root->left = root->right = NULL;
	}
	else if(data <= root->data)
		root->left = Insert(root->left,data);
	else 
		root->right = Insert(root->right,data);
	return root;
}

int main() {
	/*Code To Test the logic
	  Creating an example tree
	                    5
			   / \
			  3   10
			 / \   \
			1   4   11
    */
	Node* root = NULL;
	root = Insert(root,5); root = Insert(root,10);
	root = Insert(root,3); root = Insert(root,4); 
	root = Insert(root,1); root = Insert(root,11);

	// Deleting node with value 5, change this value to test other cases
	root = Delete(root,5);

	//Print Nodes in Inorder
	cout<<"Inorder: ";
	Inorder(root);
	cout<<"\n";
}

Hello All, why do we need to

Node* FindMin(Node* root){ while(root->left != NULL) root = root->left; return root;}

find Min and use of Inorder here when we have already used it in delete Function.? I have a doubt on this.?
can anybody help me here.? And one more mistake is char data is used instead of integer(int data). so kindly change it.?

What need of temp?
Isn't it enough
root=root->left
for the case 2

There is another issue with the code, in your example you've been deleting elements from the right sub tree, if you try to delete from left subtree, your FindMin function will fail.

def minValue(node, data):
current = node
if (data < node.data):

loop down to find the right most leaf

while(current.right is not None):
current = current.right
elif (data > node.data):

loop down to find the left most leaf

while(current.left is not None):
current = current.left

return current.data

This is what I did to fix it.

We need to FindMax in order to delete from left subtree as Max from left subtree would be Inorder Predecesor

Hello All, why do we need to

Node* FindMin(Node* root){ while(root->left != NULL) root = root->left; return root;}
find Min and use of Inorder here when we have already used it in delete Function.? I have a doubt on this.? can anybody help me here.? And one more mistake is char data is used instead of integer(int data). so kindly change it.?

Inorder function to print the tree in order list like this : 1 3 4 5 10 11

in the code given by mycodeschool, there is a logical bug, which can cause a Segmentation Error
root=NULL, and root = root->right; this will not be reflected outside the function,
it should be *root=NULL, and the function definition should be like this struct Node* Delete(struct Node **root, int data)

my approach without recursive (gfg practice):-

void delLeafnode(Node *cur, Node *prev, int X)
{
if(Xdata) prev->left = NULL;
else prev->right = NULL;
}

void deloneNode(Node *cur, Node *prev, int X)
{
if(Xdata)
{
if(cur->left) prev->left = cur->left;
else prev->left = cur->right;
}
else
{
if(cur->left) prev->right = cur->left;
else prev->right = cur->right;
}

}

Node *findmin(Node *root, int X)
{
Node *cur = root->right;
Node *prev = root;
Node *temp;
while(cur!=NULL)
{
if(!cur->left)
{
temp = cur;
if(!cur->left && !cur->right) delLeafnode(cur, prev, X) ;
else if(!cur->left || !cur->right) deloneNode(cur, prev, X);
}
prev = cur;
cur = cur->left;
}
return temp;
}

Node *deleteNode(Node *root, int X) {
Node *cur = root;
Node *prev = NULL;

if(root->data==X && (!root || (!root->left && !root->right))) return NULL;
while(cur!=NULL)
{
    if(cur->data == X)
    {
        if(!cur->left && !cur->right)
        {
            delLeafnode(cur, prev, X);
        }
        
        else if(!cur->left || !cur->right)
        {
            deloneNode(cur, prev, X);
        }
        
        else if(cur->left && cur->right)
        {
            Node *node = findmin(cur, X);
            cur->data = node->data;
        }
    }
    
    prev = cur;
    if(X<cur->data) cur = cur->left;
    else cur = cur->right;
}
return root;

}

in the code given by mycodeschool, there is a logical bug, which can cause a Segmentation Error
root=NULL, and root = root->right; this will not be reflected outside the function,
it should be *root=NULL, and the function definition should be like this struct Node* Delete(struct Node **root, int data)

How this will not be reflected outside the function if he has equated the function to the original root variable by root = Delete(root,5);?
By using pointer to a pointer you are creating a mess for yourself, nothing else.
Better check this with the Search_Node function.

Hey, I just want everyone to know that after Deleting a node from a BST, better check if the node is present or not by the Search_Node Function. Call the Search_Node function in the main function and check if the value returned by the Search_Node function is true or false.
Here is the Definition:
bool Search_Node(BstNode *root, int data)
{
if(root==NULL)
return false;
if(data==root->data)
return true;
else if(data>root->data)
return Search_Node(root->right, data);
else
return Search_Node(root->left, data);
}

Here's how you can check:
if(Search_Node(root, 20)==true) // here 20 is the data for the deleted node
printf("FOUND\n");
else
printf("NOT FOUND\n");

It should return temp once deleted root in single child case