isBST.cpp

/*
For the purposes of this challenge, we define a binary search tree to be a binary tree with the following ordering properties:

    The value of every node in a node's left subtree is less than the data value of that node.
    The value of every node in a node's right subtree is greater than the data value of that node.

Given the root node of a binary tree, can you determine if it's also a binary search tree?

Complete the function in your editor below, which has parameter: a pointer to the root of a binary tree. It must return a boolean denoting whether or not the binary tree is a binary search tree. You may have to write one or more helper functions to complete this challenge.

Note: We do not consider a binary tree to be a binary search tree if it contains duplicate values.

Input Format

You are not responsible for reading any input from stdin. Hidden code stubs will assemble a binary tree and pass its root node to your function as an argument.

Constraints

Output Format

You are not responsible for printing any output to stdout. Your function must return true if the tree is a binary search tree; otherwise, it must return false. Hidden code stubs will print this result as a Yes or No answer on a new line.

Sample Input

tree

Sample Output

Yes

Explanation

The tree in the diagram satisfies the ordering property for a Binary Search Tree, so we print Yes.
*/

// Credit : Geek For Geeks
//http://www.geeksforgeeks.org/a-program-to-check-if-a-binary-tree-is-bst-or-not/

/* Hidden stub code will pass a root argument to the function below. Complete the function to solve the challenge. Hint: you may want to write one or more helper functions.  

The Node struct is defined as follows:
   struct Node {
      int data;
      Node* left;
      Node* right;
   }
*/
   bool checkBSTHelper(Node *root, int min, int max) {
       
       if (!root)
           return true;
       
       if (root->data < min || root->data > max) {
           return false;
       }
      
       return (checkBSTHelper(root->left, min, root->data-1) && checkBSTHelper(root->right, root->data+1, max));
   }

   bool checkBST(Node* root) {   
       return (checkBSTHelper(root, 0, 10000));
   }