LeetCode Solutions

Algorithms

#	Problem	Solution	Difficulty	Topics
1	Two Sum	C#	Easy	Array, Hash Table
2	Add Two Numbers	C#	Medium	Linked List, Math, Recursion
3	Longest Substring Without Repeating Characters	C#	Medium	Hash Table, String, Sliding Window
4	Median of Two Sorted Arrays	C#	Hard	Array, Binary Search, Divide and Conquer
14	Longest Common Prefix	C#	Easy	Array, String, Trie
19	Remove Nth Node From End of List	C#	Medium	Linked List, Two Pointers
20	Valid Parentheses	C#	Easy	String, Stack
21	Merge Two Sorted Lists	C#	Easy	Linked List, Recursion
24	Swap Nodes in Pairs	C#	Medium	Linked List, Recursion
26	Remove Duplicates from Sorted Array	C#	Easy	Array, Two Pointers
27	Remove Element	C#	Easy	Array, Two Pointers
28	Find the Index of the First Occurrence in a String	C#	Easy	Two Pointers, String, String Matching
33	Search in Rotated Sorted Array	C#	Medium	Array, Binary Search
34	Find First and Last Position of Element in Sorted Array	C#	Medium	Array, Binary Search
36	Valid Sudoku	C#	Medium	Array, Hash Table, Matrix
49	Group Anagrams	C#	Medium	Array, Hash Table, String, Sorting
50	Pow(x, n)	C#	Medium	Math, Recursion
54	Spiral Matrix	C#	Medium	Array, Matrix, Simulation
61	Rotate List	C#	Medium	Linked List, Two Pointers
66	Plus One	C#	Easy	Array, Math
67	Add Binary	C#	Easy	Math, String, Bit Manipulation, Simulation
69	Sqrt(x)	C#	Easy	Math, Binary Search
70	Climbing Stairs	C#	Easy	Math, Dynamic Programming, Memoization
88	Merge Sorted Array	C#	Easy	Array, Two Pointers, Sorting
94	Binary Tree Inorder Traversal	C#	Easy	Stack, Tree, Depth-First Search, Binary Tree
95	Unique Binary Search Trees II	C#	Medium	Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree
101	Symmetric Tree	C#	Easy	Tree, Depth-First Search, Breadth-First Search, Binary Tree
102	Binary Tree Level Order Traversal	C#	Medium	Tree, Breadth-First Search, Binary Tree
104	Maximum Depth of Binary Tree	C#	Easy	Tree, Depth-First Search, Breadth-First Search, Binary Tree
105	Construct Binary Tree from Preorder and Inorder Traversal	C#	Medium	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
106	Construct Binary Tree from Inorder and Postorder Traversal	C#	Medium	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
112	Path Sum	C#	Easy	Tree, Depth-First Search, Breadth-First Search, Binary Tree
116	Populating Next Right Pointers in Each Node	C#	Medium	Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree
117	Populating Next Right Pointers in Each Node II	C#	Medium	Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree
118	Pascal's Triangle	C#	Easy	Array, Dynamic Programming
119	Pascal's Triangle II	C#	Easy	Array, Dynamic Programming
133	Clone Graph	C#	Medium	Hash Table, Depth-First Search, Breadth-First Search, Graph
136	Single Number	C#	Easy	Array, Bit Manipulation
138	Copy List with Random Pointer	C#	Medium	Hash Table, Linked List
141	Linked List Cycle	C#	Easy	Hash Table, Linked List, Two Pointers
142	Linked List Cycle II	C#	Medium	Hash Table, Linked List, Two Pointers
144	Binary Tree Preorder Traversal	C#	Easy	Stack, Tree, Depth-First Search, Binary Tree
145	Binary Tree Postorder Traversal	C#	Easy	Stack, Tree, Depth-First Search, Binary Tree
150	Evaluate Reverse Polish Notation	C#	Medium	Array, Math, Stack
151	Reverse Words in a String	C#	Medium	Two Pointers, String
153	Find Minimum in Rotated Sorted Array	C#	Medium	Array, Binary Search
154	Find Minimum in Rotated Sorted Array II	C#	Hard	Array, Binary Search
155	Min Stack	C#	Medium	Stack, Design
160	Intersection of Two Linked Lists	C#	Easy	Hash Table, Linked List, Two Pointers
162	Find Peak Element	C#	Medium	Array, Binary Search
167	Two Sum II - Input array is sorted	C#	Medium	Array, Two Pointers, Binary Search
189	Rotate Array	C#	Medium	Array, Math, Two Pointers
200	Number of Islands	C#	Medium	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
202	Happy Number	C#	Easy	Hash Table, Math, Two Pointers
203	Remove Linked List Elements	C#	Easy	Linked List, Recursion
205	Isomorphic Strings	C#	Easy	Hash Table, String
206	Reverse Linked List	C#	Easy	Linked List, Recursion
209	Minimum Size Subarray Sum	C#	Medium	Array, Binary Search, Sliding Window, Prefix Sum
217	Contains Duplicate	C#	Easy	Array, Hash Table, Sorting
219	Contains Duplicate II	C#	Easy	Array, Hash Table, Sliding Window
225	Implement Stack using Queues	C#	Easy	Stack, Design, Queue
226	Invert Binary Tree	C#	Easy	Tree, Depth-First Search, Breadth-First Search, Binary Tree
232	Implement Queue using Stacks	C#	Easy	Stack, Design, Queue
234	Palindrome Linked List	C#	Easy	Linked List, Two Pointers, Stack, Recursion
236	Lowest Common Ancestor of a Binary Tree	C#	Medium	Tree, Depth-First Search, Binary Tree
278	First Bad Version	C#	Easy	Binary Search, Interactive
279	Perfect Squares	C#	Medium	Math, Dynamic Programming, Breadth-First Search
283	Move Zeroes	C#	Easy	Array, Two Pointers
287	Find the Duplicate Number	C#	Medium	Array, Two Pointers, Binary Search, Bit Manipulation
297	Serialize and Deserialize Binary Tree	C#	Hard	String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree
328	Odd Even Linked List	C#	Medium	Linked List
344	Reverse String	C#	Easy	Two Pointers, String
347	Top K Frequent Elements	C#	Medium	Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect
349	Intersection of Two Arrays	C#	Easy	Array, Hash Table, Two Pointers, Binary Search, Sorting
350	Intersection of Two Arrays II	C#	Easy	Array, Hash Table, Two Pointers, Binary Search, Sorting
367	Valid Perfect Square	C#	Easy	Math, Binary Search
374	Guess Number Higher or Lower	C#	Easy	Binary Search, Interactive
380	Insert Delete GetRandom O(1)	C#	Medium	Array, Hash Table, Math, Design, Randomized
383	Ransom Note	C#	Easy	Hash Table, String, Counting
387	First Unique Character in a String	C#	Easy	Hash Table, String, Queue, Counting
394	Decode String	C#	Medium	String, Stack, Recursion
410	Split Array Largest Sum	C#	Hard	Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum
412	Fizz Buzz	C#	Easy	Math, String, Simulation
414	Third Maximum Number	C#	Easy	Array, Sorting
430	Flatten a Multilevel Doubly Linked List	C#	Medium	Linked List, Depth-First Search, Doubly-Linked List
448	Find All Numbers Disappeared in an Array	C#	Easy	Array, Hash Table
454	4Sum II	C#	Medium	Array, Hash Table
485	Max Consecutive Ones	C#	Easy	Array
498	Diagonal Traverse	C#	Medium	Array, Matrix, Simulation
509	Fibonacci Number	C#	Easy	Math, Dynamic Programming, Recursion, Memoization
542	01 Matrix	C#	Medium	Array, Dynamic Programming, Breadth-First Search, Matrix
557	Reverse Words in a String III	C#	Easy	Two Pointers, String
599	Minimum Index Sum of Two Lists	C#	Easy	Array, Hash Table, String
622	Design Circular Queue	C#	Medium	Array, Linked List, Design, Queue
652	Find Duplicate Subtrees	C#	Medium	Hash Table, Tree, Depth-First Search, Binary Tree
658	Find K Closest Elements	C#	Medium	Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)
700	Search in a Binary Search Tree	C#	Easy	Tree, Binary Search Tree, Binary Tree
704	Binary Search	C#	Easy	Array, Binary Search
705	Design HashSet	C#	Easy	Array, Hash Table, Linked List, Design, Hash Function
706	Design HashMap	C#	Easy	Array, Hash Table, Linked List, Design, Hash Function
707	Design Linked List	C#	Medium	Linked List, Design
719	Find K-th Smallest Pair Distance	C#	Hard	Array, Two Pointers, Binary Search, Sorting
724	Find Pivot Index	C#	Easy	Array, Prefix Sum, Weekly Contest 58
733	Flood Fill	C#	Easy	Array, Depth-First Search, Breadth-First Search, Matrix, Weekly Contest 60
739	Daily Temperatures	C#	Medium	Array, Stack, Monotonic Stack, Weekly Contest 61
744	Find Smallest Letter Greater Than Target	C#	Easy	Array, Binary Search, Weekly Contest 62
747	Largest Number At Least Twice of Others	C#	Easy	Array, Sorting, Weekly Contest 64
752	Open the Lock	C#	Medium	Array, Hash Table, String, Breadth-First Search, Weekly Contest 64
771	Jewels and Stones	C#	Easy	Hash Table, String, Weekly Contest 69
779	K-th Symbol in Grammar	C#	Medium	Math, Bit Manipulation, Recursion, Weekly Contest 70
841	Keys and Rooms	C#	Medium	Depth-First Search, Breadth-First Search, Graph, Weekly Contest 86
876	Middle of the Linked List	C#	Easy	Linked List, Two Pointers, Weekly Contest 95
905	Sort Array By Parity	C#	Easy	Array, Two Pointers, Sorting, Weekly Contest 102
941	Valid Mountain Array	C#	Easy	Array, Weekly Contest 111
977	Squares of a Sorted Array	C#	Easy	Array, Two Pointers, Sorting, Weekly Contest 120
1051	Height Checker	C#	Easy	Array, Sorting, Counting Sort, Weekly Contest 138
1089	Duplicate Zeros	C#	Easy	Array, Two Pointers, Weekly Contest 141
1295	Find Numbers with Even Number of Digits	C#	Easy	Array, Math, Weekly Contest 168
1299	Replace Elements with Greatest Element on Right Side	C#	Easy	Array, Biweekly Contest 16
1342	Number of Steps to Reduce a Number to Zero	C#	Easy	Math, Bit Manipulation, Biweekly Contest 19
1346	Check If N and Its Double Exist	C#	Easy	Array, Hash Table, Two Pointers, Binary Search, Sorting, Weekly Contest 175
1480	Running Sum of 1d Array	C#	Easy	Array, Prefix Sum, Weekly Contest 193
1672	Richest Customer Wealth	C#	Easy	Array, Matrix, Weekly Contest 217
1991	Find the Middle Index in Array	C#	Easy	Array, Prefix Sum, Biweekly Contest 60
2236	Root Equals Sum of Children	C#	Easy	Tree, Binary Tree
3477	Fruits Into Baskets II	C#	Easy	Array, Binary Search, Segment Tree, Simulation, Ordered Set, Weekly Contest 440