LeetcodeCShaprDotNetCore

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LeetcodeCShaprDotNetCore

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My LeetCode Solutions in C#

LeetcodeCShaprDotNetCore 최신버젼 다운로드

최종 버전 다운로드 (.zip)

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# Leetcode C# solution and notes

I will use this repository to make notes for leetcode solutions and classify the problems by different topics.

## Solved Problem List
Total solved: 108

### microsoft-labed
ID | Difficulty | Tags | Solution | Similar Problem
-- | ---------- | ---- | -------- | ---------------
206 | Easy | Linked List | [Reverse Linked List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/206.%20Reverse%20Linked%20List.cs)
138 | Medium | LinkedList, Dictionary | [Copy List with Random Pointer](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/138.%20Copy%20List%20with%20Random%20Pointer.cs)
419 | Medium | Two dimentional array | [Battleships in a Board](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/419.%20Battleships%20in%20a%20Board.cs)
273 | Hard | Math, string | [Integer to English Words](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/273.%20Integer%20to%20English%20Words.cs)
54 | Medium | Array | [Spiral Matrix](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/54.%20Spiral%20Matrix.cs)
171 | Easy | Math | [Excel Sheet Column Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/171.%20Excel%20Sheet%20Column%20Number.cs) | 168
235 | Medium | BST | [Lowest Common Ancestor of a Binary Search Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/235.%20Lowest%20Common%20Ancestor%20of%20a%20Binary%20Search%20Tree.cs)
200 | Medium | BFS, DFS | [Number of Islands](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/200.%20Number%20of%20Islands.cs)
88 | Easy | Two pointers | [Merge Sorted Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/88.%20Merge%20Sorted%20Array.cs)
236 | Medium | Tree | [Lowest Common Ancestor of a Binary Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/236.%20Lowest%20Common%20Ancestor%20of%20a%20Binary%20Tree.cs)
48 | Medium | Array | [Rotate Image](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/48.%20Rotate%20Image.cs)
445 | Medium | LinkedList, Stack | [Add Two Numbers II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/445.%20Add%20Two%20Numbers%20II.cs)
268 | Easy | Array, Bit Manipulation | [Missing Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/268.%20Missing%20Number.cs)
1 | Easy | Array, Hash Table (Dictionary) | [Two Sum](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/1.%20Two%20Sum.cs)
186 | Medium | String | [Reverse Words in a String II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/186.%20Reverse%20Words%20in%20a%20String%20II.cs)
53 | Easy | Dynamic Programming, Divide and Conquer | [Maximum Subarray](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/53.%20Maximum%20Subarray.cs)
103 | Medium | Tree, BFS, Stack | [Binary Tree Zigzag Level Order Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/103.%20Binary%20Tree%20Zigzag%20Level%20Order%20Traversal.cs)
151 | Medium | String | [Reverse Words in a String](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/151.%20Reverse%20Words%20in%20a%20String.cs)
116 | Medium | Tree, DFS | [Populating Next Right Pointers in Each Node](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/116.%20Populating%20Next%20Right%20Pointers%20in%20Each%20Node.cs)
75 | Medium | Array, Two pointers, Sort | [Sort Colors](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/75.%20Sort%20Colors.cs)
73 | Medium | Array | [Set Matrix Zeroes](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/73.%20Set%20Matrix%20Zeroes.cs)
238 | Medium | Array | [Product of Array Except Self](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/238.%20Product%20of%20Array%20Except%20Self.cs)
237 | Easy| Linked List | [Delete Node in a Linked List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/237.%20Delete%20Node%20in%20a%20Linked%20List.cs)
121 | Easy | Array, Dynamic Programming | [Best Time to Buy and Sell Stock](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/121.%20Best%20Time%20to%20Buy%20and%20Sell%20Stock.cs)
168 | Easy | Math, char | [Excel Sheet Column Title](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/168.%20Excel%20Sheet%20Column%20Title.cs) | 171
141 | Easy | Two pointers, Linked List | [Linked List Cycle](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/141.%20Linked%20List%20Cycle.cs)
13 | Easy | String, Math | [Roman to Integer](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/13.%20Roman%20to%20Integer.cs)
98 | Medium | Tree, DFS | [Validate Binary Search Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/98.%20Validate%20Binary%20Search%20Tree.cs)
117 | Medium | Tree | [Populating Next Right Pointers in Each Node II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/117.%20Populating%20Next%20Right%20Pointers%20in%20Each%20Node%20II.cs)
21 | Easy | Linked List | [Merge Two Sorted Lists](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/21.%20Merge%20Two%20Sorted%20Lists.cs)
20 | Easy | Stack, String | [Valid Parentheses](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%204.%20Stack%20and%20Queue/20.%20Valid%20Parentheses.cs)
8 | Medium | Math, String | [String to Integer (atoi)](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/8.%20String%20to%20Integer%20(atoi).cs)
2 | Medium | LinkedList, Math | [Add Two Numbers](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/2.%20Add%20Two%20Numbers.cs)
33 | Medium | Binary Search, Array | [Search in Rotated Sorted Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/33.%20Search%20in%20Rotated%20Sorted%20Array.cs)
232 | Easy | Stack, Design | [Implement Queue using Stacks](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%204.%20Stack%20and%20Queue/232.%20Implement%20Queue%20using%20Stacks.cs)
153 | Medium | Binary Search, Array | [Find Minimum in Rotated Sorted Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/153.%20Find%20Minimum%20in%20Rotated%20Sorted%20Array.cs)
24 | Medium | Linked List | [Swap Nodes in Pairs](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/24.%20Swap%20Nodes%20in%20Pairs.cs)
173 | Medium | Tree, Stack, Degine | [Binary Search Tree Iterator](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/173.%20Binary%20Search%20Tree%20Iterator.cs)
215 | Medium | Divide and Conquer | [Kth Largest Element in an Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/215.%20Kth%20Largest%20Element%20in%20an%20Array.cs)
106 | Medium | Tree, DFS, Array | [Construct Binary Tree from Inorder and Postorder Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/106.%20Construct%20Binary%20Tree%20from%20Inorder%20and%20Postorder%20Traversal.cs)

### top-interview-questions

ID | Difficulty | Tags | Solution | Similar Problem
-- | ---------- | ---- | -------- | ---------------
2 | Medium | LinkedList, Math | [Add Two Numbers](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/2.%20Add%20Two%20Numbers.cs)
5 | Medium | string | [Longest Palindromic Substring](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/5.%20Longest%20Palindromic%20Substring.cs)
11 | Medium | Array, Two pointers | [Container With Most Water](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/11.%20Container%20With%20Most%20Water.cs)
13 | Easy | String, Math | [Roman to Integer](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/13.%20Roman%20to%20Integer.cs)
14 | Easy | String | [Longest Common Prefix](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/14.%20Longest%20Common%20Prefix.cs)
15 | Medium | Array, Two pointers | [3Sum](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/15.%203Sum.cs)
17 | Medium | string, backtracking | [Letter Combinations of a Phone Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/17.%20Letter%20Combinations%20of%20a%20Phone%20Number.cs)
19 | Medium | LinkedList,  Two Pointers | [Remove Nth Node From End of List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/19.%20Remove%20Nth%20Node%20From%20End%20of%20List.cs)
22 | Medium | BackTracking, DFS | [Generate Parentheses](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/22.%20Generate%20Parentheses.cs)
38 | Easy | String | [Count and Say](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/38.%20Count%20and%20Say.cs)
53 | Easy | Dynamic Programming, Divide and Conquer | [Maximum Subarray](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/53.%20Maximum%20Subarray.cs)
66 | Easy | Array, Math | [Plus One](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/66.%20Plus%20One.cs) | 67
67 | Easy | String, Math | [Add Binary](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/67.%20Add%20Binary.cs)
69 | Easy | Binary Search, Math | [Sqrt(x)](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/69.%20Sqrt(x).cs) | 367
70 | Easy | Dynamic Programming | [Climbing Stairs](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/70.%20Climbing%20Stairs.cs)
101 | Easy | Tree | [Symmetric Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/101.%20Symmetric%20Tree.cs)
108 | Easy | Tree, DFS | [Convert Sorted Array to Binary Search Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/108.%20Convert%20Sorted%20Array%20to%20Binary%20Search%20Tree.cs)
118 | Easy | Array, Math | [Pascal's Triangle](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/118.%20Pascal's%20Triangle.cs)
121 | Easy | Array, Dynamic Programming | [Best Time to Buy and Sell Stock](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/121.%20Best%20Time%20to%20Buy%20and%20Sell%20Stock.cs)
122 | Easy | Array | [Best Time to Buy and Sell Stock II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/122.%20Best%20Time%20to%20Buy%20and%20Sell%20Stock%20II.cs)
155 | Easy | Stack, Design | [Min Stack](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/155.%20Min%20Stack.cs)
160 | Easy | LinkedList | [Intersection of Two Linked Lists](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/160.%20Intersection%20of%20Two%20Linked%20Lists.cs)
169 | Easy | Dictionary | [Majority Element](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/169.%20Majority%20Element.cs)
171 | Easy | Math | [Excel Sheet Column Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/171.%20Excel%20Sheet%20Column%20Number.cs) | 168
172 | Easy | Math | [Factorial Trailing Zeroes](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/172.%20Factorial%20Trailing%20Zeroes.cs)
189 | Easy | Arrays, Two pointers | [Rotate Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/189.%20Rotate%20Array.cs)
198 | Easy | Dynamic Programming | [House Robber](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/198.%20House%20Robber.cs)
202 | Easy | Math, HashSet | [Happy Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/202.%20Happy%20Number.cs)
204 | Easy | Math, Array | [Count Primes](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/204.%20Count%20Primes.cs)
217 | Easy | Dictionary | [Contains Duplicate](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/217.%20Contains%20Duplicate.cs)
219 | Easy | HashMap, HashSet, Sliding window | [Contains Duplicate II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/219.%20Contains%20Duplicate%20II.cs)
268 | Easy | Array, Bit Manipulation | [Missing Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/268.%20Missing%20Number.cs)
344 | Easy | Two pointers | [Reverse String](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/344.%20Reverse%20String.cs)
349 | Easy | Two pointers, HashMap(Dictionary) | [Intersection of Two Arrays](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/349.%20Intersection%20of%20Two%20Arrays.cs)
350 | Easy | Two pointers, HashMap(Dictionary) | [Intersection of Two Arrays II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/350.%20Intersection%20of%20Two%20Arrays%20II.cs)
371 | Easy | Bit Manipulation | [Sum of Two Integers](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/371.%20Sum%20of%20Two%20Integers.cs)
387 | Easy | HashMap(Dictionary), string | [First Unique Character in a String](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/387.%20First%20Unique%20Character%20in%20a%20String.cs)
412 | Easy | Math | [Fizz Buzz](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/412.%20Fizz%20Buzz.cs)
105 | Medium | Tree, DFS, Array | [Construct Binary Tree from Preorder and Inorder Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/top-interview-questions/105.%20Construct%20Binary%20Tree%20from%20Preorder%20and%20Inorder%20Traversal.cs)

### Algorithms Basics

First, I will start from the very basic and useful part. The Leetcode Course Section, which is selected interview questions aimed for beginners who do not know algorithms or need a refresher. Learn by doing.

#### Chapter 1. Array / String (with similar problem)

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
26 | Easy| Array, Two Pointers | [Remove Duplicates from Sorted Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/26.%20Remove%20Duplicates%20from%20Sorted%20Array.cs)
27 | Easy | Array, Two Pointers | [Remove Element](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/27.%20Remove%20Element.cs)
203 | Easy | Linked List | [Remove Linked List Elements](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/203.%20Remove%20Linked%20List%20Elements.cs)
283 | Easy | Array, Two Pointers | [Move Zeroes](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/283.%20Move%20Zeroes.cs)
167 | Easy | Arra, Two Pointers, Binary Search | [Two Sum II - Input array is sorted](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/167.%20Two%20Sum%20II%20-%20Input%20array%20is%20sorted.cs)
1 | Easy | Array, Hash Table (Dictionary) | [Two Sum](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/1.%20Two%20Sum.cs)
653 | Easy | Binary search Tree, HashSet, BFS, recursion, traverse | [Two Sum IV - Input is a BST](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/653.%20Two%20Sum%20IV%20-%20Input%20is%20a%20BST.cs)
242 | Easy | Hash Table (Dictionary) | [Valid Anagram](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/242.%20Valid%20Anagram.cs)
438 | Easy | Hash Table (Dictionary), Two pointer, Sub string, Sliding window | [Find All Anagrams in a String](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/438.%20Find%20All%20Anagrams%20in%20a%20String.cs)
3 | Medium| Hash Table (Dictionary), Two pointer, Sub string, Sliding window |[Longest Substring Without Repeating Characters](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/3.%20Longest%20Substring%20Without%20Repeating%20Characters.cs)
28 | Easy | Two pointer, String | [Implement strStr()](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/28.%20Implement%20strStr().cs)
459 | Easy | String | [Repeated Substring Pattern](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/459.%20Repeated%20Substring%20Pattern.cs)
8 | Medium | Math, String | [String to Integer (atoi)](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/8.%20String%20to%20Integer%20(atoi).cs)

#### Chapter 2. Linked List (with similar problem)

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
237 | Easy| Linked List | [Delete Node in a Linked List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/237.%20Delete%20Node%20in%20a%20Linked%20List.cs)
206 | Easy | Linked List | [Reverse Linked List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/206.%20Reverse%20Linked%20List.cs)
234 | Easy | Linked List, Two Pointers | [Palindrome Linked List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/234.%20Palindrome%20Linked%20List.cs)
9 | Easy| Math | [Palindrome Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Palindrome/9.%20Palindrome%20Number.cs)
125 | Easy | Two pointers, String | [Valid Palindrome](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/125.%20Valid%20Palindrome.cs)
141 | Easy | Two pointers, Linked List | [Linked List Cycle](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/141.%20Linked%20List%20Cycle.cs)
142 | Medium | Two pointers, Linked List | [Linked List Cycle II](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/142.%20Linked%20List%20Cycle%20II.cs)
21 | Easy | Linked List | [Merge Two Sorted Lists](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/21.%20Merge%20Two%20Sorted%20Lists.cs)
88 | Easy | Two pointers | [Merge Sorted Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/88.%20Merge%20Sorted%20Array.cs)
24 | Medium | Linked List | [Swap Nodes in Pairs](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/24.%20Swap%20Nodes%20in%20Pairs.cs)

#### Chapter 3. Binary Tree

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
104 | Easy | Tree, DFS, BFS level traverse | [Maximum Depth of Binary Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/104.%20Maximum%20Depth%20of%20Binary%20Tree.cs)
110 | Easy | Tree, DFS | [Balanced Binary Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/110.%20Balanced%20Binary%20Tree.cs)
111 | Easy | Tree, DFS, Recursion | [Minimum Depth of Binary Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/111.%20Minimum%20Depth%20of%20Binary%20Tree.cs)
100 | Easy | Tree, DFS | [Same Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/100.%20Same%20Tree.cs)
112 | Easy | Tree, DFS | [Path Sum](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/112.%20Path%20Sum.cs)
437 | Easy | Tree, DFS | [Path Sum III](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/437.%20Path%20Sum%20III.cs)
257 | Easy | Tree, DFS | [Binary Tree Paths](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/257.%20Binary%20Tree%20Paths.cs)
98 | Medium | Tree, DFS | [Validate Binary Search Tree](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/98.%20Validate%20Binary%20Search%20Tree.cs)
94 | Medium | Tree, Stack | [Binary Tree Inorder Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/94.%20Binary%20Tree%20Inorder%20Traversal.cs)
144 | Medium | Tree, Stack | [Binary Tree Preorder Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/144.%20Binary%20Tree%20Preorder%20Traversal.cs)
145 | Medium | Tree, Stack | [Binary Tree Postorder Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/145.%20Binary%20Tree%20Postorder%20Traversal.cs)
102 | Medium | Tree, Queue, BFS | [Binary Tree Level Order Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/102.%20Binary%20Tree%20Level%20Order%20Traversal.cs)
-- | Easy | Tree, Recursion | [Binary Tree Traversal (Recursion)](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/Binary%20Tree%20Traversal%20(Recursion).cs)
-- | Medium | Tree, Iteration | [Binary Tree Traversal (Iteration)](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/Binary%20Tree%20Traversal%20(Iteration).cs)

#### Chapter 4. Stack and Queue

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
225 | Easy | Stack, Design | [Implement Stack using Queues](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%204.%20Stack%20and%20Queue/225.%20Implement%20Stack%20using%20Queues.cs)
232 | Easy | Stack, Design | [Implement Queue using Stacks](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%204.%20Stack%20and%20Queue/232.%20Implement%20Queue%20using%20Stacks.cs)
20 | Easy | Stack, String | [Valid Parentheses](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%204.%20Stack%20and%20Queue/20.%20Valid%20Parentheses.cs)
102 | Medium | Tree, Queue, Breadth-first Search | [Binary Tree Level Order Traversal](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%203.%20Binary%20Tree/102.%20Binary%20Tree%20Level%20Order%20Traversal.cs)

#### Chapter 5. Bit Manipulation

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
136 | Easy | Bit Manipulation n | [Single Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%205.%20Bit%20Manipulation/136.%20Single%20Number.cs)
190 | Easy | Bit Manipulation n | [Reverse Bits](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%205.%20Bit%20Manipulation/190.%20Reverse%20Bits.cs)
191 | Easy | Bit Manipulation n | [Number of 1 Bits](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%205.%20Bit%20Manipulation/191.%20Number%20of%201%20Bits.cs)
231 | Easy | Bit Manipulation n | [Power of Two](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%205.%20Bit%20Manipulation/231.%20Power%20of%20Two.cs)
342 | Easy | Bit Manipulation n | [Power of Four](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%205.%20Bit%20Manipulation/342.%20Power%20of%20Four.cs)

#### Chapter 6. Binary Search

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
278 | Easy | Binary Search | [First Bad Version](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%206.%20Binary%20Search/278.%20First%20Bad%20Version.cs)
374 | Easy | Binary Search | [Guess Number Higher or Lower(Current NO C# OJ Support)](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%206.%20Binary%20Search/374.%20Guess%20Number%20Higher%20or%20Lower.java)
35 | Easy | Binary Search, Array | [Search Insert Position](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%206.%20Binary%20Search/35.%20Search%20Insert%20Position.cs)
34 | Medium | Binary Search, Array | [Search for a Range](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%206.%20Binary%20Search/34.%20Search%20for%20a%20Range.cs)
367 | Medium | Binary Search | [Valid Perfect Square](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%206.%20Binary%20Search/367.%20Valid%20Perfect%20Square.cs)

## Other Topics

### Sorting

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
-- | Medium | Merge sort | [MergeSort](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/MergeSort.cs)
-- | Medium | Quick sort | [QuickSort](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/QuickSort.cs)
21 | Easy | Linked List | [Merge Two Sorted Lists](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/21.%20Merge%20Two%20Sorted%20Lists.cs)
88 | Easy | Two pointers | [Merge Sorted Array](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/88.%20Merge%20Sorted%20Array.cs)

### Palindrome
All the Palindrome problem's core solution is check if reverse == origin. A efficient way is to compare reverse the sencond half, and check if FirstHalf(origin) == SecondHalf(reversed).
For int, core solution is:
```csharp
while (x > rev) {
    rev = rev * 10 + x % 10;
    x = x / 10;
}
return (x == rev || x == rev / 10);
```
For string, core solution is:
```csharp
while (left <= right){
    if (char.ToLower(leftChar) 
        != char.ToLower(rightChar)){
        return false;
    }
    left++;
    right--;
}
return true;
```

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
9 | Easy| Math | [Palindrome Number](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Palindrome/9.%20Palindrome%20Number.cs)
125 | Easy | Two pointers, String | [Valid Palindrome](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/125.%20Valid%20Palindrome.cs)
234 | Easy | Linked List, Two Pointers | [Palindrome Linked List](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%202.%20Linked%20List/234.%20Palindrome%20Linked%20List.cs)

### SubString Topic

ID | Difficulty | Tags | Solution
-- | ---------- | ---- | --------
3 | Medium| Hash Table (Dictionary), Two pointer, Sub string, Sliding window |[Longest Substring Without Repeating Characters](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/3.%20Longest%20Substring%20Without%20Repeating%20Characters.cs)
438 | Easy | Hash Table (Dictionary), Two pointer, Sub string, Sliding window | [Find All Anagrams in a String](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/Chapter%201.%20Array_String/438.%20Find%20All%20Anagrams%20in%20a%20String.cs)
-- | Easy | Sliding window for sub string | [SubString Template](https://github.com/kflili/LeetcodeCShaprDotNetCore/blob/master/Algorithms%20Basics/SubString-topic/Sliding%20Window%20Template.cs)

###
13. Roman to Integer

#### Common knowledge
Symbol | I | V | X | L | C | D | M
Value  | 1 | 5 | 10 | 50 | 100 | 500 | 1000

**I** placed before **V** or **X** indicates one less,  so **IV** is 4 (5 - 1) and **IX** is 9 (10 - 9)
 
 **X** placed before **L** or **C** indicates ten less, so XL is 40 (50 - 10) and **XC** is 90 (100 - 10)
 
 **C** placed before **D** or **M** indicates a hundred less, so four hundred is **CD** (a hundred less than five 
hundred) and nine hundred is **CM** (a hundred less than a thousand)

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