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# mycodeschool/BSTDeletion_CPP.cpp

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 /* Deleting a node from Binary search tree */ #include 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"; }

### vaibhavs017 commented Jul 12, 2020

why we assign delete function to root in line 87.
it is necessary?

Yes the memory allocate in the heap section must be free. If not deleted then this may lead to program crash or memory leak

### pavan-areti commented Aug 22, 2020

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

root = root.left will just give attachment with its left pointer but here temp is referring to a minimum in the right subtree of the root;

### ghoshdipan commented Oct 3, 2020

shouldn't the second case be like this :
else if(root->right==NULL){
Node* temp=root->left;
delete root;
root=temp;
}

I think this is good as it seems logical to me. I am not clear with the source code.
And what will be the code of findMin??

### sanu-coder commented Oct 26, 2020

Very clean and clear code. Thanks..

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

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;
}
{
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)
{
return root;
}
else if(info<root->data)
{
}
else
{
}
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;
}while(true);
}
void look(node* root,int info)
{
if(root==nullptr)
{
}
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)
{
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;
}```

@snake-jazz

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

### ghost commented May 6, 2021

@snake-jazz

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

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

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 commented Sep 13, 2021

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 commented Nov 18, 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.?

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) `

### Akash2791-1 commented Apr 1, 2022

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