Leetcode

Build a Matrix With Conditions Problem

Problem You are given a positive integer k. You are also given: a 2D integer array rowConditions of size n where rowConditions[i] = [abovei, belowi], and a 2D integer array colConditions of size m where colConditions[i] = [lefti, righti]. The two arrays contain integers from 1 to k. You have to build a k x k matrix that contains each of the numbers from 1 to k exactly once. The remaining cells should have the value 0. ...

Find Valid Matrix Given Row and Column Sums Problem

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. ...

Lucky Numbers in a Matrix Problem

Problem Given an m x n matrix of distinct numbers, return all lucky numbers in the matrix in any order. A lucky number is an element of the matrix such that it is the minimum element in its row and maximum in its column. Examples Example 1: $$ matrix = \begin{bmatrix} 3 & 7 & 8 \\ 9 & 11 & 13 \\ \colorbox{green} {15} & 16 & 17 \end{bmatrix} $$ ...

Delete Nodes And Return Forest Problem

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; ...

Step-By-Step Directions From a Binary Tree Node to Another Problem

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: ...

Create Binary Tree From Descriptions Problem

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. ...

Number of Atoms Problem

Problem Given a string formula representing a chemical formula, return the count of each atom. The atomic element always starts with an uppercase character, then zero or more lowercase letters, representing the name. One or more digits representing that element’s count may follow if the count is greater than 1. If the count is 1, no digits will follow. For example, "H2O" and "H2O2" are possible, but "H1O2" is impossible. Two formulas are concatenated together to produce another formula. ...

Maximum Score From Removing Substrings Problem

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. ...

Reverse Substrings Between Each Pair of Parentheses Problem

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. ...

Find the Winner of the Circular Game Problem

Problem There are n friends that are playing a game. The friends are sitting in a circle and are numbered from 1 to n in clockwise order. More formally, moving clockwise from the ith friend brings you to the (i+1)th friend for 1 <= i < n, and moving clockwise from the nth friend brings you to the 1st friend. The rules of the game are as follows: ...