Difficulty/Medium

Problem You are given two arrays rowSum and colSum of non-negative integers where rowSum[i] is the sum of the elements in the ith row and colSum[j] is the sum of the elements of the jth column of a 2D matrix. In other words, you do not know the elements of the matrix, but you do know the sums of each row and column. Find any matrix of non-negative integers of size rowSum.length x colSum.length that satisfies the rowSum and colSum requirements. ...

Problem Given the root of a binary tree, each node in the tree has a distinct value. After deleting all nodes with a value in to_delete, we are left with a forest (a disjoint union of trees). Return the roots of the trees in the remaining forest. You may return the result in any order. Examples Example 1: graph TD; 1; 1 --- 2; 1 --- 3; 2 --- 4; 2 --- 5; 3 --- 6; 3 --- 7; ...

Problem You are given the root of a binary tree with n nodes. Each node is uniquely assigned a value from 1 to n. You are also given an integer startValue representing the value of the start node s, and a different integer destValue representing the value of the destination node t. Find the shortest path starting from node s and ending at node t. Generate step-by-step directions of such path as a string consisting of only the uppercase letters 'L', 'R', and 'U'. Each letter indicates a specific direction: ...

Problem You are given a 2D integer array descriptions where descriptions[i] = [parenti, childi, isLefti] indicates that parenti is the parent of childi in a binary tree of unique values. Furthermore, If isLefti == 1, then childi is the left child of parenti. If isLefti == 0, then childi is the right child of parenti. Construct the binary tree described by descriptions and return its root. ...

Problem Given an undirected graph represented as an adjacency matrix and an integer k, write a function to determine whether each vertex in the graph can be colored such that no two adjacent vertices share the same color using at most k colors. Examples Example 1: --- title: Input Graph --- graph LR; 0 --- 1 & 2 & 3 1 --- 2 2 --- 3 ...

Problem Implement locking in a binary tree. A binary tree node can be locked or unlocked only if all of its descendants or ancestors are not locked. Design a binary tree node class with the following methods: is_locked, which returns whether the node is locked lock, which attempts to lock the node. If it cannot be locked, then it should return false. Otherwise, it should lock it and return true. unlock, which unlocks the node. If it cannot be unlocked, then it should return false. Otherwise, it should unlock it and return true. You may augment the node to add parent pointers or any other property you would like. You may assume the class is used in a single-threaded program, so there is no need for actual locks or mutexes. Each method should run in O(h), where h is the height of the tree. ...

Problem You are given a string s and two integers x and y. You can perform two types of operations any number of times. Remove substring "ab" and gain x points. For example, when removing "ab" from "cabxbae" it becomes "cxbae". Remove substring "ba" and gain y points. For example, when removing "ba" from "cabxbae" it becomes "cabxe". Return the maximum points you can gain after applying the above operations on s. ...

Problem You are given a string s that consists of lower case English letters and brackets. Reverse the strings in each pair of matching parentheses, starting from the innermost one. Your result should not contain any brackets. Examples Example 1: Input: s = "(abcd)" Output: "dcba" Example 2: Input: s = "(u(love)i)" Output: "iloveu" Explanation: The substring "love" is reversed first, then the whole string is reversed. ...

Problem To estimate π using the Monte Carlo method, we’ll utilize the concept of randomly generating points within a square and determining how many fall inside a quarter circle. Monte Carlo Method Lets do the setup: Imagine a square with side length 2 centered at the origin, with coordinates ranging from (-1, -1) to (1, 1). Inside this square, there is a quarter circle of radius 1, also centered at the origin. The area of the square is 4 (since side length is 2), and the area of the quarter circle is (πr^2 / 4 = π/4) (since r=1). i.e. Let B be area of square, and A be area of circle $$ B = 4r^2 $$ ...

Problem Implement a job scheduler which takes in a function f and an integer n, and calls f after n milliseconds. Solution Implementing a job scheduler that invokes a function f after n milliseconds can be achieved using threading and timers Code Java import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; public class JobScheduler { private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1); public void jobScheduler(Runnable f, int n) { scheduler.schedule(f, n, TimeUnit.MILLISECONDS); } public static void main(String[] args) { JobScheduler js = new JobScheduler(); Runnable exampleFunction = new Runnable() { @Override public void run() { System.out.println("Function called!"); } }; // Call exampleFunction after 2000 milliseconds (2 seconds) js.jobScheduler(exampleFunction, 2000); } } ...