LeetCode Solutions in Java

#	Problems	Difficulty	Solutions	Key Points
1	Two Sum	Easy	📝	Hash
2	Add Two Numbers	Medium	📝	Linked List
3	Longest Substring Without Repeating Characters	Medium	📝	ASCII Array | Hash | Sliding Window
4	Median of Two Sorted Arrays	Hard	📝	Binary Search
11	Container With Most Water	Medium	📝	Two Pointers
15	3Sum	Medium	📝	Hash | Sort | Two Pointers
19	Remove Nth Node From End of List	Medium	📝	Two Pointers
20	Valid Parentheses	Easy	📝	Stack
21	Merge Two Sorted Lists	Easy	📝	Just Merge
22	Generate Parentheses	Medium	📝	Backtracking
23	Merge k Sorted Lists	Hard	📝	Min-heap | Merge Sort
25	Reverse Nodes in k-Group	Hard	📝	Reverse Every Group And Reconnect | Head Insertion to Reverse List | Dummy Node
28	Find the Index of the First Occurrence in a String	Medium	📝	KMP
33	Search in Rotated Sorted Array	Medium	📝	Binary Search
36	Valid Sudoku	Medium	📝	Hash | Boolean Array
42	Trapping Rain Water	Hard	📝	DP - Pre-compute Left Max and Right Max | Two Pointers
49	Group Anagrams	Medium	📝	Hash | Letter Count Char Array
74	Search a 2D Matrix	Medium	📝	Binary Search As 1D
76	Minimum Window Substring	Hard	📝	Sliding Window | Letter Count Array
84	Largest Rectangle in Histogram	Hard	📝	Monotonic Stack | DP
98	Validate Binary Search Tree	Medium	📝	DFS + from bottom to top + left max + right min | DFS + from top to bottom + interval
100	Same Tree	Easy	📝	Recursion | DFS | BFS
102	Binary Tree Level Order Traversal	Medium	📝	BFS
104	Invert Binary Tree	Easy	📝	Recursion | Breadth First Search With Queue
105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	📝	Recursion + hashmap
110	Balanced Binary Tree	Easy	📝	Recursion + class variable + height of every node | Recursion + pruning + height of partial node
121	Best Time to Buy and Sell Stock	Easy	📝	Sliding Window | Iteration | DP
125	Valid Palindrome	Easy	📝	Two Pointers
126	Binary Tree Maximum Path Sum	Hard	📝	DFS + maximum contribution of subtree
128	Longest Consecutive Sequence	Medium	📝	Hash | Consecutive Number
138	Copy List with Random Pointer	Medium	📝	Hash Map | Next Pointer Points to The New Node
141	Linked List Cycle	Easy	📝	Slow And Fast Pointer
146	LRU cache	Medium	📝	HashMap - Double Linked List
143	Reorder List	Medium	📝	Slow And Fast Pointer - Reverse List
150	Evaluate Reverse Polish Notation	Medium	📝	Stack
153	Find Minimum in Rotated Sorted Array	Medium	📝	Binary Search
155	Min Stack	Easy	📝	Two Stack - Min Value Stack | One Stack - 2x-min(old)<min(new)
167	Two Sum II - Input Array Is Sorted	Medium	📝	Two Pointers
199	Binary Tree Right Side View	Medium	📝	BFS
206	Reverse Linked List	Easy	📝	Pointers
208	Implement Trie (Prefix Tree)	Medium	📝	children[26] + is leaf + dummy root node
211	Design Add and Search Words Data Structure	Medium	📝	Trie (Prefix Tree) + DFS for '.'
212	Word Search II	Hard	📝	Trie (prefix tree) + DFS + backtracking + node keep the word
215	Kth Largest Element in an Array	Medium	📝	Randomized Quick Select + partition
217	Contains Duplicate	Easy	📝	Hash
226	Invert Binary Tree	Easy	📝	Recursion | Breadth First Search With Queue
230	Kth Smallest Element in a BST	Medium	📝	InOrder by recursion + List | InOrder by iteration + Stack
235	Lowest Common Ancestor of a Binary Search Tree	Medium	📝	BST
238	Product of Array Except Self	Medium	📝	Arrays
239	Sliding Window Maximum	Hard	📝	Sliding Window | Max-heap | Monotonic Queue
242	Valid Anagram	Easy	📝	Hash | Letter Count Array
271	Encode and Decode Strings 🔒	Medium	📝	Length of String
287	Find the Duplicate Number	Medium	📝	Binary Search | Linked List With Cycle - Floyd‘s Algorithm
297	Serialize and Deserialize Binary Tree	Hard	📝	DFS + preorder + null node
347	Top K Frequent Elements	Medium	📝	Min-heap
424	Longest Repeating Character Replacement	Medium	📝	Sliding Window | Hash | Letter Count Array | History Max Character Count
543	Diameter of Binary Tree	Easy	📝	Recursion + diameter and height of every node | Recursion + class variable keeping the diameter + height of every node
567	Permutation in String	Medium	📝	Sliding Window | Letter Count Array
572	Subtree of Another Tree	Easy	📝	Recursion + same tree | Preorder + serialize + KMP | Hash + Spurious Hits
621	Task Scheduler	Meidum	📝	Max-heap | max count of tasks + formula
703	Last Stone Weight	Easy	📝	Min-heap
704	Binary Search	Easy	📝	Binary Search
739	Daily Temperatures	Medium	📝	Stack
853	Car Fleet	Medium	📝	Stack | Sort
875	Koko Eating Bananas	Medium	📝	Binary Search Eating Speed
973	K Closest Points to Origin	Medium	📝	Max-heap
981	Time Based Key-Value Store	Medium	📝	Binary Search
1046	Last Stone Weight	Easy	📝	Max-heap
1448	Count Good Nodes in Binary Tree	Medium	📝	DFS + max value