From 52d1c3e421abf27f9e316eba43fff9c6302ed4cd Mon Sep 17 00:00:00 2001
From: Masoom9587 <93204893+Masoom9587@users.noreply.github.com>
Date: Fri, 21 Oct 2022 12:03:19 +0530
Subject: [PATCH] code for binary tree is a bst or not!!

solved the issue #250
---
 tree.cpp | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 tree.cpp

diff --git a/tree.cpp b/tree.cpp
new file mode 100644
index 00000000..ef19d662
--- /dev/null
+++ b/tree.cpp
@@ -0,0 +1,60 @@
+// C++ program to check if a given tree is BST.
+#include <bits/stdc++.h>
+using namespace std;
+
+/* A binary tree node has data, pointer to
+left child and a pointer to right child */
+struct Node {
+	int data;
+	struct Node *left, *right;
+
+	Node(int data)
+	{
+		this->data = data;
+		left = right = NULL;
+	}
+};
+
+bool isBSTUtil(struct Node* root, Node*& prev)
+{
+	// traverse the tree in inorder fashion and
+	// keep track of prev node
+	if (root) {
+		if (!isBSTUtil(root->left, prev))
+			return false;
+
+		// Allows only distinct valued nodes
+		if (prev != NULL && root->data <= prev->data)
+			return false;
+
+		prev = root;
+
+		return isBSTUtil(root->right, prev);
+	}
+
+	return true;
+}
+
+bool isBST(Node* root)
+{
+	Node* prev = NULL;
+	return isBSTUtil(root, prev);
+}
+
+/* Driver code*/
+int main()
+{
+	struct Node* root = new Node(3);
+	root->left = new Node(2);
+	root->right = new Node(5);
+	root->left->left = new Node(1);
+	root->left->right = new Node(4);
+
+	// Function call
+	if (isBST(root))
+		cout << "Is BST";
+	else
+		cout << "Not a BST";
+
+	return 0;
+}