checkifbst.cpp

#include<bits/stdc++.h>
using namespace std;

class node
{
    public:
        int data;
        node*left;
        node*right;

        node(int data)
        {
            this->data = data;
            this->left = NULL;
            this->right = NULL;
        }
};

int isBSTUtil(node*node,int min,int max)
{
    if(node==NULL)
    {
        return 1;
    }

    if(node->data < min || node->data > max)
    {
        return 0;
    }
    return isBSTUtil(node->left,min,node->data-1);
    return isBSTUtil(node->right,node->data+1,max);
}

int isBST(node*node)
{
    return (isBSTUtil(node,INT_MIN,INT_MAX));
}

int main()
{
    node*root = new node(4);
    root->left = new node(2);
    root->right = new node(5);
    root->left->left = new node(1);  
    root->left->right = new node(3);  
      
    if(isBST(root))  
        cout<<"Is BST";  
    else
        cout<<"Not a BST";  
          
    return 0;  

}