Trees: Is This a Binary Search Tree?

Problem Statement :

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

The data value of every node in a node's left subtree is less than the data value of that node.
The data value of every node in a node's right subtree is greater than the data value of that node.
The data value of every node is distinct.
For example, the image on the left below is a valid BST. The one on the right fails on several counts:
- All of the numbers on the right branch from the root are not larger than the root.
- All of the numbers on the right branch from node 5 are not larger than 5.
- All of the numbers on the left branch from node 5 are not smaller than 5.
- The data value 1 is repeated.

Function Description

Complete the function checkBST in the editor below. It must return a boolean denoting whether or not the binary tree is a binary search tree.

checkBST has the following parameter(s):

root: a reference to the root node of a tree to test
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.


0   <=  data  <=  10^4

Output Format

Your function must return a boolean true if the tree is a binary search tree. Otherwise, it must return false.

Solution :


                        Solution in C++ :

In   C++ :

   struct Node {
      int data;
      Node* left;
      Node* right;
bool soy=true;
int mini(int a, int b)
    return a<b ? a:b;
int maxi(int a, int b)
    return a>b ? a:b;
typedef pair<int, int> ii;
#define f first
#define s second
ii revisar(Node* root)
    ii h(-1, 10005), iz(10005,10005), de(-1,-1);
     if (root->left!=NULL)
         if (iz.s >= root->data or iz.f >= root->data) soy=false;
    if (root->right!=NULL)
        if (de.f <= root->data or de.s <= root->data) soy=false;
    return ii{mini(root->data, iz.f),maxi(root->data, de.s) };

   bool checkBST(Node* root) {
       if (root!=NULL)
       //else return false;
       return soy;

                        Solution in Java :

In   Java :

    class Node {
        int data;
        Node left;
        Node right;
    boolean checkBST(Node root) {  
        //return fasle;
        return checkBSTHelper(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
    private boolean checkBSTHelper(Node n, int min, int max) {
        if (n == null) return true;
        if ( <= min || >= max) return false;
        return checkBSTHelper(n.left, min, && checkBSTHelper(n.right,, max);

                        Solution in Python : 
In   Python3 :

""" Node is defined as
class node:
    def __init__(self, data): = data
        self.left = None
        self.right = None

def check(node, max_val = float('inf'), min_val = float('-inf')):
    if not node:
        return True
    if <= min_val or >= max_val:
        return False
    return check(node.left,, min_val) and check(node.right, max_val,

def check_binary_search_tree_(root):
    return check(root)

View More Similar Problems

Truck Tour

Suppose there is a circle. There are N petrol pumps on that circle. Petrol pumps are numbered 0 to (N-1) (both inclusive). You have two pieces of information corresponding to each of the petrol pump: (1) the amount of petrol that particular petrol pump will give, and (2) the distance from that petrol pump to the next petrol pump. Initially, you have a tank of infinite capacity carrying no petr

View Solution →

Queries with Fixed Length

Consider an -integer sequence, . We perform a query on by using an integer, , to calculate the result of the following expression: In other words, if we let , then you need to calculate . Given and queries, return a list of answers to each query. Example The first query uses all of the subarrays of length : . The maxima of the subarrays are . The minimum of these is . The secon

View Solution →


This question is designed to help you get a better understanding of basic heap operations. You will be given queries of types: " 1 v " - Add an element to the heap. " 2 v " - Delete the element from the heap. "3" - Print the minimum of all the elements in the heap. NOTE: It is guaranteed that the element to be deleted will be there in the heap. Also, at any instant, only distinct element

View Solution →

Jesse and Cookies

Jesse loves cookies. He wants the sweetness of all his cookies to be greater than value K. To do this, Jesse repeatedly mixes two cookies with the least sweetness. He creates a special combined cookie with: sweetness Least sweet cookie 2nd least sweet cookie). He repeats this procedure until all the cookies in his collection have a sweetness > = K. You are given Jesse's cookies. Print t

View Solution →

Find the Running Median

The median of a set of integers is the midpoint value of the data set for which an equal number of integers are less than and greater than the value. To find the median, you must first sort your set of integers in non-decreasing order, then: If your set contains an odd number of elements, the median is the middle element of the sorted sample. In the sorted set { 1, 2, 3 } , 2 is the median.

View Solution →

Minimum Average Waiting Time

Tieu owns a pizza restaurant and he manages it in his own way. While in a normal restaurant, a customer is served by following the first-come, first-served rule, Tieu simply minimizes the average waiting time of his customers. So he gets to decide who is served first, regardless of how sooner or later a person comes. Different kinds of pizzas take different amounts of time to cook. Also, once h

View Solution →