C++ program to find Inorder successor in a BST

BST_InorderSuccessor_CPP.cpp

/* C++ program to find Inorder successor in a BST */
#include<iostream>
using namespace std;
struct Node {
	int data;
	struct Node *left;
	struct Node *right;
};

//Function to find some data in the tree
Node* Find(Node*root, int data) {
	if(root == NULL) return NULL;
	else if(root->data == data) return root;
	else if(root->data < data) return Find(root->right,data);
	else return Find(root->left,data);
}

//Function to find Node with minimum value in a BST
struct Node* FindMin(struct Node* root) {
	if(root == NULL) return NULL;
	while(root->left != NULL)
		root = root->left;
	return root;
}

//Function to find Inorder Successor in a BST
struct Node* Getsuccessor(struct Node* root,int data) {
	// Search the Node - O(h)
	struct Node* current = Find(root,data);
	if(current == NULL) return NULL;
	if(current->right != NULL) {  //Case 1: Node has right subtree
		return FindMin(current->right); // O(h)
	}
	else {   //Case 2: No right subtree  - O(h)
		struct Node* successor = NULL;
		struct Node* ancestor = root;
		while(ancestor != current) {
			if(current->data < ancestor->data) {
				successor = ancestor; // so far this is the deepest node for which current node is in left
				ancestor = ancestor->left;
			}
			else
				ancestor = ancestor->right;
		}
		return successor;
	}
}
 
//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);

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

	// Find Inorder successor of some node. 
	struct Node* successor = Getsuccessor(root,1);
	if(successor == NULL) cout<<"No successor Found\n";
	else
    cout<<"Successor is "<<successor->data<<"\n";
}

Dear Code School;

Shouldn't the data-type for "data" in Line 59, be int? Cause the struct has "data" as int.

https://gist.github.com/mycodeschool/6515e1ec66482faf9d79#file-bst_inordersuccessor_cpp-cpp-L59

Thanks,
Anu

Yaa ur are right Anu it should be int

Hey!
Can you tell me why we didn't just use a FindMax() function for the left subtree like we used the FindMin() function for the right?
Is it because of the time complexity? But then wouldn't it take as much time as the FindMax() function?
This is really bugging me, any clarity would help!

Line 54 should be like this : cout<<root->data<<" "; //Print data
Because we are in c++ right now :D

Python version: https://github.com/rishijd/python-learning/blob/master/data-structures/trees-inorder-successor.py

Even though this was created in 2014, it is so useful today. Thank you!

shouldn't line 14 be with this greater than "else if(root->data > data) return Find(root->right,data);" instead of less than "else if(root->data < data) return Find(root->right,data);" because if a node is greater than you search right node left

Dear Code School;

Shouldn't the data-type for "data" in Line 59, be int? Cause the struct has "data" as int.

https://gist.github.com/mycodeschool/6515e1ec66482faf9d79#file-bst_inordersuccessor_cpp-cpp-L59

Thanks,
Anu

he may have written it bymistake

A more simpler program in java which takes care of both the cases

public TreeNode getSuccessor(TreeNode a, int b) {
       TreeNode res=null;
       TreeNode cur=a;
       while(cur!=null){
           if(cur.val>b){
               res=cur;
               cur=cur.left;
            }else{
               cur=cur.right;
           }
       }
       return res;
   }

Dear Code School;

Shouldn't the data-type for "data" in Line 59, be int? Cause the struct has "data" as int.

https://gist.github.com/mycodeschool/6515e1ec66482faf9d79#file-bst_inordersuccessor_cpp-cpp-L59

Thanks,
Anu

No, It's right. It would be int when that function returns return root->data;

Dear Code School;
Shouldn't the data-type for "data" in Line 59, be int? Cause the struct has "data" as int.
https://gist.github.com/mycodeschool/6515e1ec66482faf9d79#file-bst_inordersuccessor_cpp-cpp-L59
Thanks,
Anu

No, It's right. It would be int when that function returns return root->data;

No Adarsh , Anu is not asking about the return type but the data type! And it is supposed to be int since integer(int) is passed to the insert function, not a character(char).

Is find function necessary?

We also need to write some condition to handle the maximium element in the BST, in this case 11, if we try to find inorder successor of 11, this gives 5 as the answer. So adding 1 more if condition to the Getsuccessor() will work fine.
if(data == maxelementintree) return NULL

Line 54 should be like this : cout<<root->data<<" "; //Print data
Because we are in c++ right now :D

Yes it should be in C++ print form

A more simpler program in java which takes care of both the cases

public TreeNode getSuccessor(TreeNode a, int b) {
       TreeNode res=null;
       TreeNode cur=a;
       while(cur!=null){
           if(cur.val>b){
               res=cur;
               cur=cur.left;
            }else{
               cur=cur.right;
           }
       }
       return res;
   }

awesome