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@mycodeschool
Last active April 14, 2024 04:05
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/* 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";
}
@sanu-coder
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Very clean and clear code. Thanks..

@rahuldeepattri
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rahuldeepattri commented Jan 19, 2021

A small bug, the Case 2 logic should be like this (ignoring delete statements):

             //Case 1 node has no children
            if (root.left == null && root.right == null) {
                root = null; 
            }
            // Case 2 Only one child
            else if (root.left != null && root.right == null) {
                root = root.left;
            } else if (root.right != null && root.left == null) {
                root = root.right;
            }
            //Case 3 Both the child are present
            else {

The original logic is <3

@ajaypep
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ajaypep commented Jan 27, 2021

I can't seem to delete the root node, if I did it breaks the link in the right sub tree.

#include<iostream>
#include<sstream>
struct node
{
    int data;
    node *left,*right;
};

class bst
{
    node *root;
    public:
    bst()
    {
        root=nullptr;
    }
    node* addNode(node *root,int info)
    {
        if(root==nullptr)
        {
            root=new node;
            root->data=info;
            root->left=nullptr;
            root->right=nullptr;
            std::cout<<"Inserted "<<root->data<<"\n";
            return root;
        }
        else if(info==root->data)
        {
            std::cout<<"Element already exists\n";
            return root;
        }
        else if(info<root->data)
        {
            root->left=addNode(root->left,info);
        }
        else
        {
            root->right=addNode(root->right,info);
        }
        return root;
    }
    void insert()
    {
        std::string s;
        int i;
        do
        {
            std::cout<<"Enter q to quit\n";
            std::cout<<"Enter a unique number : ";
            std::cin>>s;
            if(s=="q")
            {
                std::cout<<"Exited\n";
                return;
            }
            std::stringstream int_str(s);
            int_str>>i;
            root=addNode(root,i);
        }while(true);
    }
    void look(node* root,int info)
    {
        if(root==nullptr)
        {
            std::cout<<"Node not found\n";
        }
        else if(info==root->data)
        {
            std::cout<<"Node found containing "<<info<<"\n";
        }
        else if(info<root->data)
        {
            look(root->left,info);
        }
        else
        {
            look(root->right,info);
        }
    }
    void search()
    {
        int i;
        std::string s;
        do
        {
            std::cout<<"Enter q to quit\n";
            std::cout<<"Enter a number to search  : ";
            std::cin>>s;
            if(s=="q")
            {
                std::cout<<"Exited\n";
                return;
            }
            std::stringstream int_str(s);
            int_str>>i;
            look(root,i);
        }while(true);
    }
    node* findMin(node *root)
    {
        while(root->left!=nullptr)
        { 
		root=root->left;
        }
	return root;
    }
    node* remove(node* root,int info)
    {
        //first search the node
        if(root==nullptr)
        {
            std::cout<<"Not found\n";
            return root;
        }
        else if(info<root->data)
        {
            root->left=remove(root->left,info);
        }
        else if(info>root->data)
        {
            root->right=remove(root->left,info);
        }
        //found the element
        else
        {
            //it has no child
            if(root->left==nullptr && root->right==nullptr)
            {
                delete root;
                std::cout<<"Deleted "<<root->data<<"\n";
                return root;
            }
            //it has one child(right)
            else if(root->left==nullptr)
            {
                node* tmp=root->right;
                delete root;
                std::cout<<"Deleted "<<root->data<<"\n";
                return tmp;
            }
            //it has one child(left)
            else if(root->right==nullptr)
            {
                node* tmp=root->left;
                delete root;
                std::cout<<"Deleted "<<root->data<<"\n";
                return tmp;
            }
            //it has two children
            else
            {
                node* tmp=findMin(root);
                root->data=tmp->data;
                root->right=remove(root->right,tmp->data);
            }
        }
        return root;
    }
    void del()
    {
        int i;
        std::string s;
        do
        {
            std::cout<<"Enter q to quit\n";
            std::cout<<"Enter a number = ";
            std::cin>>s;
            if(s=="q")
            {
                std::cout<<"Exited\n";
                return;
            }
            std::stringstream int_str(s);
            int_str>>i;
            root=remove(root,i);
        }while(true);
    }
};
int main()
{
    bst myt;
    myt.insert();
    myt.search();
    myt.del();
    myt.search();
    return 0;
}

@mmatros
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mmatros commented Apr 24, 2021

@snake-jazz

delete root;
std::cout<<"Deleted "<<root->data<<"\n";

Access to already deleted object

@ajaypep
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ajaypep commented May 6, 2021

@snake-jazz

delete root;
std::cout<<"Deleted "<<root->data<<"\n";

Access to already deleted object

Hey, thanks for replying to my post. Actually I've moved to Java so I'm practicing data structures using Java, still appreciate it.

@Bhabesh142
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Bhabesh142 commented Jun 6, 2021

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.?

@jankivaghasiya
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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

@phongvu009
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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

@AryanGitHub
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AryanGitHub commented Feb 5, 2022

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)

@Akash2791-1
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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;

}

@vinamrgrover
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vinamrgrover commented Apr 14, 2022

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.

@vinamrgrover
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vinamrgrover commented Apr 14, 2022

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");

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