From 1b532aec48f67d4348e7437a8a52c9c16592bb71 Mon Sep 17 00:00:00 2001
From: Harshit Jain <hj03111996@gmail.com>
Date: Sun, 17 Oct 2021 19:30:26 +0530
Subject: [PATCH] Create is_tree_bst.cpp

---
 is_tree_bst.cpp | 75 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 is_tree_bst.cpp

diff --git a/is_tree_bst.cpp b/is_tree_bst.cpp
new file mode 100644
index 0000000..61997fb
--- /dev/null
+++ b/is_tree_bst.cpp
@@ -0,0 +1,75 @@
+#include<bits/stdc++.h>
+
+using namespace std;
+
+/* A binary tree node has data,
+pointer to left child and
+a pointer to right child */
+class node
+{
+	public:
+	int data;
+	node* left;
+	node* right;
+	
+	/* Constructor that allocates
+	a new node with the given data
+	and NULL left and right pointers. */
+	node(int data)
+	{
+		this->data = data;
+		this->left = NULL;
+		this->right = NULL;
+	}
+};
+
+int isBSTUtil(node* node, int min, int max);
+
+/* Returns true if the given
+tree is a binary search tree
+(efficient version). */
+int isBST(node* node)
+{
+	return(isBSTUtil(node, INT_MIN, INT_MAX));
+}
+
+/* Returns true if the given
+tree is a BST and its values
+are >= min and <= max. */
+int isBSTUtil(node* node, int min, int max)
+{
+	/* an empty tree is BST */
+	if (node==NULL)
+		return 1;
+			
+	/* false if this node violates
+	the min/max constraint */
+	if (node->data < min || node->data > max)
+		return 0;
+	
+	/* otherwise check the subtrees recursively,
+	tightening the min or max constraint */
+	return
+		isBSTUtil(node->left, min, node->data-1) && // Allow only distinct values
+		isBSTUtil(node->right, node->data+1, max); // Allow only distinct values
+}
+
+
+/* Driver code*/
+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;
+}
+
+// This code is contributed by rathbhupendra