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47 articles

MANG Problem #8: Alien Dictionary (Hard)

1. Problem Statement There is a new alien language that uses the English alphabet. However, the order of the letters is unknown to you. You are given a list of strings words from the alien language dictionary, where the…

Apr 26, 20263 min read

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MANG Problem #15: Basic Calculator II (Hard)

1. Problem Statement Given a string s which represents an expression, evaluate this expression and return its value. The expression string contains only non-negative integers, +, -, `, / operators, and empty spaces. The…

Apr 26, 20263 min read

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MANG Problem #29: Burst Balloons (Hard)

1. Problem Statement You are given n balloons, indexed from 0 to n - 1. Each balloon is painted with a number on it represented by an array nums. You are asked to burst all the balloons. If you burst the i-th balloon, yo…

Apr 26, 20263 min read

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MANG Problem #46: Count Vowels Permutation (Hard)

1. Problem Statement Given an integer n, your task is to count how many strings of length n can be formed under the following rules: - Each character is a lower case vowel ('a', 'e', 'i', 'o', 'u'). - 'a' may only be fol…

Apr 26, 20263 min read

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MANG Problem #43: Cut Off Trees for Golf Event (Hard)

1. Problem Statement You are asked to cut off all the trees in a forest for a golf event. The forest is represented as an m x n matrix. In this matrix: - 0 means the cell cannot be walked through. - 1 means the cell can…

Apr 26, 20264 min read

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MANG Problem #42: Design In-Memory File System (Hard)

1. Problem Statement Design a data structure that simulates an in-memory file system. Implement the FileSystem class: - List ls(String path) - void mkdir(String path) - void addContentToFile(String filePath, String conte…

Apr 26, 20263 min read

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MANG Problem #39: Design Search Autocomplete System (Hard)

1. Problem Statement Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character '#'). You are given a string array sentences and an integer arr…

Apr 26, 20264 min read

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MANG Problem #13: Edit Distance (Hard)

1. Problem Statement Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: 1. Insert a character 2. De…

Apr 26, 20263 min read

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MANG Problem #24: Employee Free Time (Hard)

1. Problem Statement We are given a list schedule of employees, which represents the working time for each employee. Each employee has a list of non-overlapping Intervals, and these intervals are sorted in increasing ord…

Apr 26, 20263 min read

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MANG Problem #34: Find Median from Data Stream (Hard)

1. Problem Statement The median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value, and the median is the mean of the two middle values. Implement the MedianFinder c…

Apr 26, 20263 min read

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MANG Problem #27: First Missing Positive (Hard)

1. Problem Statement Given an unsorted integer array nums, return the smallest missing positive integer. You must implement an algorithm that runs in $O(n)$ time and uses $O(1)$ auxiliary space. Input: nums = [3,4,-1,1]…

Apr 26, 20263 min read

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MANG Problem #33: Insert Interval (Hard)

1. Problem Statement You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by sta…

Apr 26, 20263 min read

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MANG Problem #14: K-th Smallest in Lexicographical Order (Hard)

1. Problem Statement Given two integers n and k, return the k-th lexicographically smallest integer in the range [1, n]. Input: n = 13, k = 2 Output: 10 Explanation: The lexicographical order is [1, 10, 11, 12, 13, 2, 3,…

Apr 26, 20263 min read

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MANG Problem #26: Largest Rectangle in Histogram (Hard)

1. Problem Statement Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the histogram. Input: heights = [2,1,5,6,2,3]…

Apr 26, 20263 min read

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MANG Problem #16: LFU Cache Design (Hard)

1. Problem Statement Design and implement a data structure for a Least Frequently Used (LFU) cache. - LFUCache(int capacity): Initializes the object with the capacity of the data structure. - int get(int key): Gets the v…

Apr 26, 20263 min read

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MANG Problem #22: Longest Increasing Path in a Matrix (Hard)

1. Problem Statement Given an m x n integers matrix, return the length of the longest increasing path in matrix. From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonal…

Apr 26, 20263 min read

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MANG Problem #11: Longest Valid Parentheses (Hard)

1. Problem Statement Given a string containing just the characters ( and ), return the length of the longest valid (well-formed) parentheses substring. Input: s = ")()())" Output: 4 (The valid substring is "()()") 2. App…

Apr 26, 20263 min read

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MANG Problem #5: LRU Cache Design (Hard)

1. Problem Statement Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: - LRUCache(int capacity): Initialize the cache with positive size capacity. -…

Apr 26, 20263 min read

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MANG Problem #41: Making A Large Island (Hard)

1. Problem Statement You are given an n x n binary matrix grid. You are allowed to change at most one 0 to be 1. Return the size of the largest island in grid after applying this operation. An island is a 4-directionally…

Apr 26, 20264 min read

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MANG Problem #25: Maximal Rectangle (Hard)

1. Problem Statement Given a rows x cols binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area. Input: Output: 6 2. Approach: Matrix-to-Histogram Reduction Finding a re…

Apr 26, 20263 min read

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MANG Problem #45: Maximize Score After N Operations (Hard)

1. Problem Statement You are given nums, an array of positive integers of size 2 n. You must perform n operations. In the i-th operation (1-indexed), you will: - Choose two elements, x and y. - Receive a score of i gcd(x…

Apr 26, 20264 min read

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MANG Problem #35: Maximum Profit in Job Scheduling (Hard)

1. Problem Statement We have n jobs, where every job is scheduled to be done from startTime[i] to endTime[i], obtaining a profit of profit[i]. You're given the startTime, endTime, and profit arrays, return the maximum pr…

Apr 26, 20263 min read

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MANG Problem #2: Median of Two Sorted Arrays (Hard)

1. Problem Statement Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays. - Constraint: The overall run time complexity should be $O(\log (m+n))$. 2. Approach:…

Apr 26, 20263 min read

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MANG Problem #4: Merge K Sorted Lists (Hard)

1. Problem Statement You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Input: lists = [[1,4,5],[1,3,4],[2…

Apr 26, 20263 min read

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MANG Problem #23: Minimum Window Subsequence (Hard)

1. Problem Statement Given strings S and T, find the minimum (contiguous) substring W of S, such that T is a subsequence of W. If there is no such window in S that contains all characters in T after keeping the order of…

Apr 26, 20263 min read

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MANG Problem #37: Minimum Number of K Consecutive Bit Flips (Hard)

1. Problem Statement You are given a binary array nums and an integer k. A k-bit flip is choosing a subarray of length k from nums and simultaneously changing every 0 in the subarray to 1, and every 1 in the subarray to…

Apr 26, 20263 min read

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MANG Problem #12: N-Queens (Hard)

1. Problem Statement The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Return all distinct solutions to the n-queens puzzle. 2. Approach: Row-by-Row…

Apr 26, 20263 min read

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MANG Problem #38: Palindrome Pairs (Hard)

1. Problem Statement Given a list of unique words, return all the pairs of the distinct indices (i, j) in the given list, so that the concatenation of the two words words[i] + words[j] is a palindrome. Input: words = ["a…

Apr 26, 20263 min read

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MANG Problem #48: Parallel Courses III (Hard)

1. Problem Statement You are given an integer n, which indicates that there are n courses labeled from 1 to n. You are also given a 2D integer array relations where relations[j] = [prevCoursej, nextCoursej], denoting tha…

Apr 26, 20263 min read

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MANG Problem #49: Prefix and Suffix Search (Hard)

1. Problem Statement Design a special dictionary that searches the words in it by a prefix and a suffix. Implement the WordFilter class: - WordFilter(String[] words) Initializes the object with the words in the dictionar…

Apr 26, 20263 min read

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MANG Problem #44: Race Car (Hard)

1. Problem Statement Your car starts at position 0 and speed +1 on an infinite number line. Your car can go into negative positions. You can issue the instructions 'A' (Accelerate) or 'R' (Reverse): - 'A': position += sp…

Apr 26, 20263 min read

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MANG Problem #31: Regular Expression Matching (Hard)

1. Problem Statement Given an input string s and a pattern p, implement regular expression matching with support for '.' and '' where: - '.' Matches any single character. - '' Matches zero or more of the preceding elemen…

Apr 26, 20263 min read

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MANG Problem #7: Reverse Nodes in k-Group (Hard)

1. Problem Statement Given the head of a linked list, reverse the nodes of the list k at a time and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the num…

Apr 26, 20263 min read

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MANG Problem #36: Serialize and Deserialize BST (Hard)

1. Problem Statement Serialization is converting a data structure to a sequence of bits. Design an algorithm to serialize and deserialize a Binary Search Tree (BST). The encoded string should be as compact as possible. 2…

Apr 26, 20263 min read

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MANG Problem #21: Serialize and Deserialize Binary Tree (Hard)

1. Problem Statement Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to b…

Apr 26, 20263 min read

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MANG Problem #50: Sliding Puzzle (Hard)

1. Problem Statement On an 2 x 3 board, there are five tiles labeled from 1 to 5, and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of th…

Apr 26, 20264 min read

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MANG Problem #6: Sliding Window Maximum (Hard)

1. Problem Statement You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time…

Apr 26, 20263 min read

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MANG Problem #30: Smallest Range Covering Elements from K Lists (Hard)

1. Problem Statement You have k lists of sorted integers in non-decreasing order. Find the smallest range that includes at least one number from each of the k lists. A range [a, b] is smaller than [c, d] if b - a < d - c…

Apr 26, 20263 min read

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MANG Problem #10: Sudoku Solver (Hard)

1. Problem Statement Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: 1. Each of the digits 1-9 must occur exactly once in each row. 2. Each…

Apr 26, 20263 min read

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MANG Problem #40: Swim in Rising Water (Hard)

1. Problem Statement You are given an n x n integer matrix grid where each value grid[i][j] represents the elevation at that point (i, j). The rain starts to fall. At time t, the depth of the water everywhere is t. You c…

Apr 26, 20264 min read

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MANG Problem #1: Trapping Rain Water (Hard)

1. Problem Statement Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining. Input: height = [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 2.…

Apr 26, 20263 min read

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MANG Problem #9: Binary Tree Maximum Path Sum (Hard)

1. Problem Statement A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path d…

Apr 26, 20263 min read

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MANG Problem #47: Valid Arrangement of Pairs (Hard)

1. Problem Statement You are given a 0-indexed 2D integer array pairs where pairs[i] = [starti, endi]. An arrangement of pairs is valid if for every index i where 1 <= i < pairs.length, we have end{i-1} == starti. Return…

Apr 26, 20264 min read

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MANG Problem #32: Word Break II (Hard)

1. Problem Statement Given a string s and a dictionary of strings wordDict, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Input: s =…

Apr 26, 20262 min read

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MANG Problem #17: Word Ladder (Hard)

1. Problem Statement A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: - Every adjacent pair of words differs b…

Apr 26, 20263 min read

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MANG Problem #28: Word Ladder II (Hard)

1. Problem Statement Given two words, beginWord and endWord, and a dictionary wordList, return all the shortest transformation sequences from beginWord to endWord. Each sequence should be a list of words [beginWord, s1,…

Apr 26, 20263 min read

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MANG Problem #3: Word Search II (Hard)

1. Problem Statement Given an m x n board of characters and a list of strings words, return all words on the board. Each word must be constructed from letters of sequentially adjacent cells, where adjacent cells are hori…

Apr 26, 20263 min read

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