UMPIRE Problem Solutions

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Linked Lists

• Reverse a Doubly Linked List
• Swap Nodes In Pairs
• Rotate List
• LRU Cache
• Spiral Matrix IV
• Reverse Nodes in k-Group
• Remove Duplicates from Sorted List
• Linked List Cycle
• Merge Two Sorted Lists
• Remove Duplicates from Sorted List II
• Remove Nth Node from End of List
• Add Two Numbers
• Middle of the Linked List
• Reverse Linked List II
• Reverse Linked List
• Linked List Cycle II
• Remove Linked List Elements
• Palindrome Linked Lists
• Add Two Numbers II

Stacks

• Min Stack
• Implement Queue Using Stacks
• Find a Celebrity
• Dinner Plate Stacks
• Evaluate Reverse Polish Notation
• Valid Parentheses
• Sort a stack using a temporary stack
• Score of Parentheses
• Validate Stack Sequences
• Decode String
• Number of People That Can Be Seen in a Grid
• Crawler Log Folder

Queues

• Number of Recent Calls
• Implement Queue Using Stacks
• Implement Stack Using Queue
• Moving Average from Data Stream
• Number of Students Unable to Eat Lunch
• New UMPIRE Problem: Queues

Heaps

• Kth Largest Element in a Stream
• K Closest Points to the Origin
• Find K Pairs with Smallest Sums
• Last Stone Weight
• Kth Largest Element in an Array

Hash Tables

• Brick Wall
• Word Pattern
• Encode and Decode TinyURL
• Single Number
• Element with a frequency of K
• Longest Consecutive Sequence
• Majority Element
• Roman to Integer
• Destination City
• Number of Arithmetic Triplets

Arrays and Strings

• Substring
• Valid Palindrome
• Reverse Words in a String
• String to Integer (ATOI)
• Plus One
• Run Length Encoding
• Shortest Unsorted Subarray
• Word Frequency
• Reverse a String
• Shifting Letters
• Set Matrix Zeros
• Longest Repeating Character Replacement
• Group Anagrams
• Trapping Rain Water
• Basic Calculator
• Asteroid Collision
• Two Sum
• Integer to String
• Reverse Words in a String II
• Squares of a Sorted Array
• Unique Number of Occurrences
• Merge Sorted Array
• Word Frequency
• Find Subsequence of Length K With the Largest Sum
• Is Subsequence
• Sort Colors
• Product of Array Except Self
• Container With Most Water
• Merge Intervals
• 3Sum
• Crawler Log Folder
• Shortest Distance to a Character

2D-Array

• Flood Fill
• 01 Matrix
• Word Search II
• Rotting Oranges
• Spiral Matrix
• Number of Islands
• Island Perimeter
• Transpose Matrix
• Flipping an Image
• Rotate Image
• Number of Islands
• Max Area of Island
• Battleships in a Board
• Search a 2D Matrix
• Lucky Numbers in a Matrix
• Pacific Atlantic Water Flow

Binary Search

• Binary Search
• First Bad Version
• Sqrt(x)
• Find Minimum in Rotated Sorted Array
• Search in Rotated Sorted Array
• Guess Number Higher or Lower
• Koko Eating Bananas

Trees

• Min Depth of Binary Trees
• Binary Tree Pruning
• Vertical Order Traversal of a Binary Tree
• Find Duplicate Subtrees
• Most Frequent Subtree Sum
• Convert Sorted Array to Binary Search Tree
• Flatten Binary Tree to Linked List
• Find Largest Value in Each Tree Row
• Same Trees
• Insert into a Binary Search Tree
• Print Binary Tree
• Binary Tree Paths
• Convert Sorted List to BST
• Invert Binary Tree
• Maximum Depth of Binary Tree
• Diameter of Binary Tree
• Balanced Binary Tree
• Binary Tree Inorder Traversal
• Symmetric Tree
• Minimum Depth of Binary Tree
• Path Sum
• Binary Tree Preorder Traversal
• Sum of Left Leaves
• Binary Tree Level Order Traversal
• Lowest Common Ancestor of a Binary Tree
• Binary Tree Right Side View
• Construct Binary Tree from Preorder and Inorder Traversal
• Distribute Coins in Binary Tree
• Path Sum III
• Kth Smallest Element in a BST
• Count Good Nodes in Binary Tree
• Validate Binary Search Tree
• All Nodes Distance K in Binary Tree
• Add One Row to Tree

Graphs

• Time Needed to Inform All Employees
• Number of Islands
• Flood Fill
• 01 Matrix
• Word Search
• Rotting Oranges
• Accounts Merge
• Maximal Network Rank
• Number of Connected Components
• Keys and Rooms
• Minimum Knight Moves
• Shortest Path to Get Food
• Course Schedule
• Minimum Height Trees
• Word Ladder
• Reconstruct Itinerary
• Swim in Rising Water
• Cheapest Flights Within K Stops
• Finish All Tasks
• Evaluate Division
• Most Stones Removed
• Clone Graph
• Connecting Cities With Minimum Cost
• The Earliest Moment When Everyone Become Friends
• Accounts Merge
• Maximal Network Rank
• Clone Graph
• Find Eventual Safe States
• Find the Town Judge
• Find Center of Star Graph
• Find if Path Exists in Graph
• Number of Good Paths
• The Time When the Network Becomes Idle

Greedy

• Largest Number
• Task Scheduler
• Rabbits In The Forest
• Advantage Shuffle

Dynamic Programming

• Maximum Subarray
• Word Break
• Longest Palindromic Substring
• Unique Paths
• Maximal Rectangle
• Climbing Stairs
• Minimum Path Sum
• House Robber
• Fibonacci Number
• Min Cost Climbing Stairs
• Best Time to Buy and Sell Stock
• Pascal's Triangle
• Pascal's Triangle II
• Shopping Offers
• Dungeon Game

Backtracking

• Finish All Tasks
• Generate Parentheses
• Subsets
• Word Search
• Path with Maximum Gold
• N Queens
• Matchsticks to Square

Recursion with Memoization

• Integer Replacement
• Can I Win

Miscellaneous

• Valid Palindrome
• Next Prime
• Valid Palindrome II
• Pow(x,n)
• Permutations
• Power of Two
• Power of Three
• Power of Four
• Fibonacci Number