Binary Search Tree Validation - Amazon Top Interview Questions
Problem Statement :
Given a binary tree root, return whether it's a binary search tree. A binary tree node is a binary search tree if : All nodes on its left subtree are smaller than node.val All nodes on its right subtree are bigger than node.val All nodes hold the these properties. Constraint n ≤ 100,000 where n is the number of nodes in root Example 1 Input root = [3, [2, null, null], [9, [7, [4, null, null], [8, null, null]], [12, null, null]]] Output True Example 2 Input root = [3, [1, null, null], [5, [4, null, [7, null, null]], [6, null, null]]] Output False Explanation This is not a binary search tree because the 7 is not smaller than 5.
Solution :
Solution in C++ :
bool isBST(Tree* root, int lo, int hi) {
if (root == NULL) return 1;
if (root->val < lo or root->val > hi) return 0;
return isBST(root->left, lo, root->val) and isBST(root->right, root->val, hi);
}
bool solve(Tree* root) {
return isBST(root, INT_MIN, INT_MAX);
}
Solution in Python :
# class Tree:
# def __init__(self, val, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def solve(self, root):
def inorder(root):
if root is None:
return True
nonlocal l
left = inorder(root.left)
if (l > root.val) or not left:
return False
l = root.val
return inorder(root.right)
l = -float("inf")
return inorder(root)
View More Similar Problems
Polynomial Division
Consider a sequence, c0, c1, . . . , cn-1 , and a polynomial of degree 1 defined as Q(x ) = a * x + b. You must perform q queries on the sequence, where each query is one of the following two types: 1 i x: Replace ci with x. 2 l r: Consider the polynomial and determine whether is divisible by over the field , where . In other words, check if there exists a polynomial with integer coefficie
View Solution →Costly Intervals
Given an array, your goal is to find, for each element, the largest subarray containing it whose cost is at least k. Specifically, let A = [A1, A2, . . . , An ] be an array of length n, and let be the subarray from index l to index r. Also, Let MAX( l, r ) be the largest number in Al. . . r. Let MIN( l, r ) be the smallest number in Al . . .r . Let OR( l , r ) be the bitwise OR of the
View Solution →The Strange Function
One of the most important skills a programmer needs to learn early on is the ability to pose a problem in an abstract way. This skill is important not just for researchers but also in applied fields like software engineering and web development. You are able to solve most of a problem, except for one last subproblem, which you have posed in an abstract way as follows: Given an array consisting
View Solution →Self-Driving Bus
Treeland is a country with n cities and n - 1 roads. There is exactly one path between any two cities. The ruler of Treeland wants to implement a self-driving bus system and asks tree-loving Alex to plan the bus routes. Alex decides that each route must contain a subset of connected cities; a subset of cities is connected if the following two conditions are true: There is a path between ever
View Solution →Unique Colors
You are given an unrooted tree of n nodes numbered from 1 to n . Each node i has a color, ci. Let d( i , j ) be the number of different colors in the path between node i and node j. For each node i, calculate the value of sum, defined as follows: Your task is to print the value of sumi for each node 1 <= i <= n. Input Format The first line contains a single integer, n, denoti
View Solution →Fibonacci Numbers Tree
Shashank loves trees and math. He has a rooted tree, T , consisting of N nodes uniquely labeled with integers in the inclusive range [1 , N ]. The node labeled as 1 is the root node of tree , and each node in is associated with some positive integer value (all values are initially ). Let's define Fk as the Kth Fibonacci number. Shashank wants to perform 22 types of operations over his tree, T
View Solution →