[](https://leetcode.com/ParthoBiswas007/) Leetcode.com and 77 Algoexpert.io problems with solutions using Swift and Python

This repo contains my solutions to algorithmic problems in leetcode.com and algoexpert.io written in Swift and Python.
Here is my leetcode profile.

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About • Topics • Tips • LeetCode.com • AlgoExpert.io • References

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About

I have solved quite a number of problems from several topics. See the below table for further details.

Languages

• Python, Swift

Topics

• Binary Search
• Binary Search Tree
• Binary Tree(Segment Tree)
• N-aray Tree(Trie, Binary Indexed Tree)
• Graph(Dijkstra, Union Find, Kruskal, Prim's, Minimum Spanning Tree, Topological Ordering...etc)
• Stack
• Queue
• Array
• Sorting
• Hash Table
• Heap
• Linked list
• Bit Operation
• Dynamic programming
• Backtracking(Permutations & Combinations & Subsets...etc)
• Math
• and more...

Questions from

• Leetcode
• Algoexpert.io
• Glassdoor
• Interviews
• ...

My other related repos

• Coding Interview Patterns
• OOD Patterns Principles
• Swift Cheat Sheet
• iOS Architecture by Example

My leetcode account

• ParthoBiswas007

Tips

• Whenever you solve a new question with some new techniques/algorithms, try to solve atleast 2 similar problem in a row. This way, your understanding to the new techniques/algorithms will be better.
• ...

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LeetCode

Arrays , HashMap

#	Title	Solution	Tutorial	Level	Remarks
01	1. Two Sum	Python, Swift	---	---	✅ 📌 ⭐ 😭 🧐 😎
02	485. Max Consecutive Ones	Swift
03	476. Number Complement	Swift
04	461. Hamming Distance	Swift
05	9. Palindrome Number	Python
06	88. Merge Sorted Array	Python
07	811. Subdomain Visit Count	Python
08	771. Jewels and Stones	Python
09	414. Third Maximum Number	Python
10	259. 3Sum Smaller	Python
11	16. 3Sum Closest	Python
12	15. 3Sum	Python
13	118. Pascal's Triangle	Python
14	119. Pascal's Triangle II	Python
15	238. Product of Array Except Self	Python
16	724. Find Pivot Index	Python
17	747. Largest Number At Least Twice of Others	Python
18	581. Shortest Unsorted Continuous Subarray	Python
19	904. Fruit Into Baskets	Python	Article, Video 1, Video 2
20	56. Merge Intervals	Python	Article
21	334. Increasing Triplet Subsequence	Python	---	Medium	---
22	792. Number of Matching Subsequences	Python	Official	Medium	Very tricky. Check again

String

#	Title	Solution	Tutorial	Level	Remarks
01	3. Longest Substring Without Repeating Characters
02	412. Fizz Buzz	Swift
03	937. Reorder Log Files	Python
03	929. Unique Email Addresses	Python
04	7. Reverse Integer	Python
05	13. Roman to Integer	Python
06	125. Valid Palindrome	Python
07	161. One Edit Distance	Python
08	1119. Remove Vowels from a String	Python
09	344. Reverse String	Python
10	482. License Key Formatting	Python

Linked List

#	Title	Solution	Tutorial	Level	Remarks
01	2. Add Two Numbers	Swift
02	707. Design Linked List	Python
03	21. Merge Two Sorted Lists	Python
04	206. Reverse Linked List	Python
05	24. Swap Nodes in Pairs	Python

Stack, Queue

#	Title	Solution	Tutorial	Level	Remarks
01	20. Valid Parentheses	Python
02	155. Min Stack	Python
03	84. Largest Rectangle in Histogram	Python	Video 01, Video 02, Article 01, Article 02	Hard	📌 Need to revise

Sorting

#	Title	Solution	Tutorial	Level	Remarks
01	912. Sort an Array (Merge Sort)	Python

Binary Search

#	Title	Solution	Tutorial	Level	Remarks
01	704. Binary Search	Python
03	240. Search a 2D Matrix II	Python	Video 01, Video 02
04	74. Search a 2D Matrix	Python	Video 01, Video 02
05	1011. Capacity To Ship Packages Within D Days	Python	Discussion 1, Discussion 2, Discussion 3	Medium	Difficult to spot the pattern, revise again
06	410. Split Array Largest Sum	Python	Article 01	Hard	📌 Not done
07	4. Median of Two Sorted Arrays	Python	Article 01, Video 1	Hard	📌 Classic problem
08	981. Time Based Key-Value Store	Python	Article 01	Medium	📌
09	222. Count Complete Tree Nodes	Python	Theory, Official Solution, Fantastic idea!	Medium	📌 BS within BS

Binary Search Tree

#	Title	Solution	Tutorial	Level	Remarks
01	701. Insert into a Binary Search Tree	Python
02	700. Search in a Binary Search Tree	Python
03	270. Closest Binary Search Tree Value	Python

N-Ary Tree

#	Title	Solution	Tutorial	Level	Remarks
01	589. N-ary Tree Preorder Traversal	Python
02	590. N-ary Tree Postorder Traversal	Python
03	429. N-ary Tree Level Order Traversal	Python
06	559. Maximum Depth of N-ary Tree	Python
07	431. Encode N-ary Tree to Binary Tree	Python	Explanation
08	428. Serialize and Deserialize N-ary Tree	Python

Tree

#	Title	Solution	Tutorial	Level	Remarks
01	450. Delete Node in a BST	Python
02	98. Validate Binary Search Tree	Python
03	94. Binary Tree Inorder Traversal	Python
04	144. Binary Tree Preorder Traversal	Python
05	145. Binary Tree Postorder Traversal	Python
06	226. Invert Binary Tree	Python
07	101. Symmetric Tree	Python
08	102. Binary Tree Level Order Traversal	Python
09	107. Binary Tree Level Order Traversal II	Python
10	103. Binary Tree Zigzag Level Order Traversal	Python
11	695. Max Area of Island	Python
12	104. Maximum Depth of Binary Tree	Python	Explanation
13	100. Same Tree	Python
14	11. Minimum Depth of Binary Tree	Python		Easy	---
15	110. Balanced Binary Tree	Python	Video 1, Article 1, Article 2	Easy	---
16	315. Count of Smaller Numbers After Self	Python	Article 1, Article 2, Vid 1, Vid 2	Hard (Very)	📌 It's a very hard and advanced problem and need to check again. But before that, learn more on Binary Indexed Tree, Segment Tree, Self-Balancing Trees like AVL-Tree and Red-Black Tree also on Bit Manipulation

Heaps

#	Title	Solution	Tutorial	Level	Remarks
01	253_Meeting_Rooms_II	Python	Official	Medium	---
02	347. Top K Frequent Elements	Python	Helper 1, Helper 2, heapq, Counter	Medium	---

Tries

#	Title	Solution	Tutorial	Level	Remarks
01	208. Implement Trie (Prefix Tree)	Python
02	211. Add and Search Word. Data structure design	Python	Video 01, Video 02
03	642. Design Search Autocomplete System	Python	Article 01, Video 01	Hard	---

Graphs

#	Title	Solution	Tutorial	Level	Remarks

Union Find / Disjoint Sets

#	Title	Solution	Tutorial	Level	Remarks
01	200. Number of Islands	Python

Recursion, Iteration

#	Title	Solution	Tutorial	Level	Remarks
01	509. Fibonacci Number	Python
02	50. Pow(x, n)	Python
00	It's a general topics which has been covered on Backtracking and graph problems	---	---	---	---

Backtracking

#	Title	Solution	Tutorial	Level	Remarks
01	211. Add and Search Word. Data structure design	Python	Video 01, Video 02
02	37. Sudoku Solver	Python	Video 01, Video 02
03	52. N-Queens II	Python	Video 01, Video 02
04	784. Letter Case Permutation	Python	---	Easy	Backtracking Fundamentals
05	22. Generate Parentheses	Python	Video 1, Article 1	Medium	Backtracking Fundamentals
06	17. Letter Combinations of a Phone Number	Python	Video 1, Video 2 - paid course, Article 1	Medium	Backtracking Fundamentals
07	46. Permutations	Python	Video 1 - paid course, Article 1, Article 2	Medium	Backtracking Fundamentals
08	39. Combination Sum	Python	Article 1, Article 2	Medium	Backtracking Fundamentals
09	79. Word Search	Python	Article 1	Medium	Backtracking Fundamentals
10	78. Subsets	Python	Video 1, Video 2, Video 3, Article 1	Medium	📌 TODO: check bit manipulation
11	77. Combinations	Python	Video 1 - paid course	Medium	📌 TODO: Not done. Hard to grasp. Check again
12	1066. Campus Bikes II	Python	Algo Notes	Medium	📌 TODO: Backtracking solution is getting TLE. Solve it and implement it with DP also
13	1087. Brace Expansion	Python	---	Medium	📌 ---
14	1219. Path with Maximum Gold	Python	---	Medium	📌 ---

Greedy

#	Title	Solution	Tutorial	Level	Remarks
01	1055. Shortest Way to Form String	Python	Art 1, Art 2	Medium	📌 Check BS approach again
02	1057. Campus Bikes	Python	Video 01, Article 01	Medium	📌 Solve 1066. Campus Bikes II using DP, DFS and Priority Queue
03	1007. Minimum Domino Rotations For Equal Row	Python	Official, Article 01	Medium	📌 Hard to spot if it is a Greedy
04	406. Queue Reconstruction by Height	Python	Article 1, Article 2	Medium	📌 Fundamentals
05	621. Task Scheduler	Python	Ex 1, Ex 2, Vid 1	Medium	📌 Extremely tricky. Not done. Check later
06	392. Is Subsequence	Python	Ex 1, Ex 3	Easy	📌
07	55. Jump Game	Python	Official , Art 1	Medium	📌 Must Check. Learned a lot
08	45. Jump Game II	Python	Vid 1, Vid 2, Vid 3, Art 1	Hard	📌

Dynamic Programming

#	Title	Solution	Tutorial	Level	Remarks
01	53. Maximum Subarray	Python
02	518. Coin Change 2	Python
03	322. Coin Change	Python
04	72. Edit Distance	Python	Video 01
05	70. Climbing Stairs	Python
06	96. Unique Binary Search Trees	Python	Video 01, Video 02
07	95. Unique Binary Search Trees II	Python
08	221. Maximal Square	Python	Video 01, Video 02
09	85. Maximal Rectangle	Python	Video 01
10	42. Trapping Rain Water	Python	Article 01	Hard	📌 Check stack and 2 pointers based solutions
11	300. Longest Increasing Subsequence	Python	Article 01	Medium	📌 Need to check Binary Search approach, which is a lot harder
12	1143. Longest Common Subsequence	Python	---	Medium	📌 Classic DP
13	5. Longest Palindromic Substring	Python	---	Medium	📌 Classic DP
14	1066. Campus Bikes II	Python		Medium	📌 TODO: Backtracking solution is getting TLE. Solve it and implement it with DP also
15	121. Best Time to Buy and Sell Stock	Python	Vid 1	Easy	Fundamental
16	122. Best Time to Buy and Sell Stock II	Python	Video 01	Easy	More like Greedy
17	123. Best Time to Buy and Sell Stock III	Python	Vid 1, Vid 2	Hard	Fundamental
18	188. Best Time to Buy and Sell Stock IV	Python	Vid 1, Vid 2	Hard	Getting "Memory Limit Exceeded"
19	309. Best Time to Buy and Sell Stock with Cooldown	Python	Must, Art0, Art1, Must 2 , Art 2, Art 3,	Medium	Very tricky, must check again. Couldn't solve
20	714. Best Time to Buy and Sell Stock with Transaction Fee	Python	Must Read , Art 2	Medium	More like Greedy, but DP

Bit Manipulation

#	Title	Solution	Tutorial	Level	Remarks
01	78. Subsets	Python	Video 1, Video 2, Video 3	Medium	📌 TODO: code it in all 4 ways. First complete DFS, BFS, Bit Manipulation and some easy back tracking problem. ⭐ 😭 Didn't understand, check again
02	136. Single Number	Python	---	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
03	461. Hamming Distance	Python	---	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
04	371. Sum of Two Integers	Python	Video 1, Atricle 1	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
05	169. Majority Element	Python	Atricle 1	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
06	191. Number of 1 Bits	Python	Article 1	Easy	📌 The key here is to practice bit operation
07	137. Single Number II	Python	1, 2, 3, Check discussion	Medium	⭐ 😭 Didn't understand, check again
08	389. Find the Difference	Python	---	Easy	📌
09	231. Power of Two	Python	Official, Signed number representations	Easy	📌 Learned few very important binary logic properties
10	268. Missing Number	Python	Official	Easy	📌 Learned few very important binary logic properties
11	187. Repeated DNA Sequences	Python	Official	Medium	⭐ 😭 Didn't understand, check again

Mathematics

#	Title	Solution	Tutorial	Level	Remarks
01	1118. Number of Days in a Month	Python

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AlgoExpert

77 Problems

Arrays

#	Title	Solution	Tutorial	Level	Remarks
01	Two_Number_Sum	Swift, Python
02	Three_Number_Sum	Python
03	Smallest_Difference	Python
04	Four_Number_Sum	Python
05	Subarray_Sort	Python
06	Largest_Range	Python
07	Min_Rewards	Python
08	Zigzag_Traverse	Python
08	Apartment_Hunting	Python
09	Calendar_Matching	Python

Binary Search Tree

#	Title	Solution	Tutorial	Level	Remarks
01	BST_Construction_Iterative	Python
02	BST_Construction_Recursive	Python
03	Validate_BST	Python
04	Find_Closest_Value_in_BST	Python
05	BST_Traversal	Python

Binary Tree

#	Title	Solution	Tutorial	Level	Remarks
01	Invert_Binary_Tree	Python
02	Max_Path_Sum_In_Binary_Tree	Python
03	Iterative_In-order_Traversal	Python

Dynamic Programming

#	Title	Solution	Tutorial	Level	Remarks
01	Number_Of_Ways_To_Make_Changes	Python
02	Minimum_Number_Of_Coins_For_Change	Python
03	Levenshtein_Distance	Python
04	Min_Number_Of_Jumps	Python	Video 1
05	Max_Sum_Increasing_Subsequence	Python
06	Longest_Common_Subsequence	Python	Video 1
07	Water_Area	Python
08	Knapsack_Problem	Python
09	Disk_Stacking	Python
10	Numbers_In_Pi	Python
11	Maximum_Subset_Sum_With_No_Adjacent_Element	Python
12	Max_Profit_With_K_Transactions	Python
13	Palindrome_Partitioning_Min_Cuts	Python
14	Longest_Increasing_Subsequence	Python	Video 1, Video 2, , Video 3

Famous Algorithm

#	Title	Solution	Tutorial	Level	Remarks
01	Kadane's_Algorithm	Python
02	Topological_Sort	Python

Graphs

#	Title	Solution	Tutorial	Level	Remarks
01	Youngest_Common_Ancestor	Python
02	Single_Cycle_Check	Python
03	River_Sizes	Python
04	Depth_First_Search	Python
05	Breadth_First_Search	Python
06	Boggle_Board	Python

Heaps

#	Title	Solution	Tutorial	Level	Remarks
01	Min_Heap_Construction	Python	Video 1
02	Continuous_Median	Python	Video 1, Video 2

Linked List

#	Title	Solution	Tutorial	Level	Remarks
01	Remove_Kth_Node_From_End	Python
02	Linked_List_Construction	Python
03	Find_Loop	Python
04	Reverse_Linked_List	Python
05	LRU_Cache	Python

Recursion

#	Title	Solution	Tutorial	Level	Remarks
01	Powerset	Python
02	Permutations	Python
03	Nth_Fibonacci	Python
04	Product_Sum	Python
05	Lowest_Common_Manager	Python
06	Number_Of_Possible_Binary_Tree_Topologies	Python

Searching

#	Title	Solution	Tutorial	Level	Remarks
01	Search_In_Sorted_Matrix	Python
02	Find_Three_Largest_Number	Python
03	Binary_Search	Python
04	Shifted_Binary_Search	Python
05	Search_For_Range	Python
06	Quick_Select (Kth smallest/largest element)	Python

Sorting

#	Title	Solution	Tutorial	Level	Remarks
01	Selection_Sort	Python
02	Insertion_Sort	Python
03	Bubble_Sort	Python
04	Quick_Sort	Python	Video 1
05	Heap_Sort	Python
06	Merge_Sort	Python

Stacks

#	Title	Solution	Tutorial	Level	Remarks
01	Balanced Bracket	Python
02	Min_Max_Stack_Construction	Python

String

#	Title	Solution	Tutorial	Level	Remarks
01	Palindrom_Check	Python
02	Longest_Palindromic_Substring	Python
03	Caesar_Cipher_Encryptor	Python
04	Longest_Substring_Without_Duplication	Python
05	Underscorify_Substring	Python
06	Pattern_Matcher	Python

Tries

#	Title	Solution	Tutorial	Level	Remarks
01	Suffix_Trie_Construction	Python
02	Multi_String_Search	Python

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References

Some helpful links, channels, tutorials, blogs.

Strategies

1. How a Googler solves coding problems
2. Nail Every Coding Interview by Becoming Asymmetrical

Courses/Books

1. Data Structures in Python: An Interview Refresher
2. Grokking the Coding Interview: Patterns for Coding Questions
3. Grokking Dynamic Programming Patterns for Coding Interviews
4. Coding Interview Class
5. Competitive Programmer’s Handbook

Channels

1. Tushar Roy - Coding Made Simple
2. Back To Back SWE

Graphs (Tree, BST, BIT, Segment Tree, etc)

1. Fenwick Tree or Binary Indexed Tree - youtube
2. Binary Indexed Tree or Fenwick Tree - geeksforgeeks
3. Binary Indexed Tree or Fenwick Tree - topcoder
4. Segment Tree Range Minimum Query - youtube
5. Segment Tree | Set 1 (Sum of given range) - geeksforgeeks
6. Practical Data Structures for Frontend Applications: When to use Segment Trees
7. What is the difference between a binary indexed tree and a segment tree?
8. How does one decide when to use a Segment Tree or Fenwick Tree?
9. What are the differences between segment trees, interval trees, binary indexed trees and range trees?

Bit Manipulation

1. Bit Manipulation - youtube
2. Conversion of Binary, Octal and Hexadecimal Numbers
3. Your guide to Bit Manipulation
4. Python Bitwise Operators
5. Add Two Numbers Without The "+" Sign (Bit Shifting Basics)
6. Binary Arithmetic
7. 1’s and 2’s complement of a Binary Number
8. What is “2's Complement”?
9. Bits manipulation (Important tactics)
10. Bit Manipulation
11. Python Bitwise Operators
12. XOR - The magical bitwise operator
13. A summary: how to use bit manipulation to solve problems easily and efficiently - leetcode
14. Bit Manipulation 4% of LeetCode Problems
15. Coding Interview University - Bitwise operations
16. Mask (computing)
17. What is Bit Masking?
18. Understanding Bit masks
19. Bitmasks: A very esoteric (and impractical) way of managing booleans
20. Hacker’s Delight - BOOK
21. Bitwise operators — Facts and Hacks
22. Signed number representations

Dynamic Programming

1. Tabulation vs Memoization
2. Memoization vs Tabulation

Greedy

1. Greedy Method - Introduction
2. Introduction to Greedy Method
3. Introduction to Greedy Algorithms | GeeksforGeeks
4. Basics of Greedy Algorithms
5. When to try greedy algorithms on problems?
6. How to spot a “greedy” algorithm?

DP VS Greedy

1. Greedy Algorithm and Dynamic Programming
2. Greedy approach vs Dynamic programming
3. What is the difference between dynamic programming and greedy approach?

Backtracking

1. Backtracking - wiki
2. Backtracking | Introduction
3. Introduction to Backtracking - Brute Force Approach
4. Branch and Bound Introduction
5. The Backtracking Blueprint: The Legendary 3 Keys To Backtracking Algorithms
6. Backtracking explained
7. Foundation of algorithms - Chapter 5 (Backtracking) notes
8. Backtracking Search Algorithms

Recursion

1. Learning to think with recursion, part 1
2. Learning to think with recursion, part 2
3. What makes a data structure recursive?
4. Binary Tree as a Recursive Data Structure
5. Recursion Visualizer - use Viz Mode
6. Thinking Recursively in Python
7. Breaking out of a recursive function?
8. Why does recursion return the first call in the stack and not the last?