Here is the list of solved problems. Language images are clickable and lead to the solution file.

No.	Description (link to Leetcode)	Explanation	Lang
2	Add Two Numbers
3	Longest Substring Without Repeating Characters
5	Longest Palindromic Substring
7	Reverse Integer
13	Roman to Integer
25	Reverse Nodes in k-Group
30	Substring with Concatenation of All Words
33	Search in Rotated Sorted Array
34	Find First and Last Position of Element in Sorted Array
35	Search Insert Position
41	First Missing Positive
50	Pow(x, n)
60	Permutation Sequence
62	Unique Paths
67	Add Binary
69	Sqrt(x)
74	Search a 2D Matrix
86	Partition List
88	Merge Sorted Array
89	Gray Code
92	Reverse Linked List II
102	Binary Tree Level Order Traversal
114	Flatten Binary Tree to Linked List
118	Pascal’s Triangle
119	Pascal’s Triangle II
136	Single Number
137	Single Number II
153	Find Minimum in Rotated Sorted Array
167	Two Sum II - Input Array Is Sorted
172	Factorial Trailing Zeroes
200	Number of Islands
202	Happy Number
204	Count Primes
206	Reverse Linked List
215	Kth Largest Element in an Array
234	Palindrome Linked List
235	Lowest Common Ancestor of a Binary Search Tree
236	Lowest Common Ancestor of a Binary Tree
240	Search a 2D Matrix II
242	Valid Anagram
260	Single Number III
263	Ugly Number
264	Ugly Number II
278	First Bad Version
279	Perfect Squares
304	Range Sum Query 2D - Immutable
307	Range Sum Query - Mutable
315	Count of Smaller Numbers After Self
326	Power of Three
342	Power of Four
350	Intersection of Two Arrays II
367	Valid Perfect Square
374	Guess Number Higher or Lower
377	Combination Sum IV
378	Kth Smallest Element in a Sorted Matrix
383	Ransom Note
387	First Unique Character in a String
429	N-ary Tree Level Order Traversal
441	Arranging Coins
462	Minimum Moves to Equal Array Elements II
623	Add One Row to Tree
633	Sum of Square Numbers
637	Average of Levels in Binary Tree
668	Kth Smallest Number in Multiplication Table
695	Max Area of Island
704	Binary Search
729	My Calendar I
733	Flood Fill
744	Find Smallest Letter Greater Than Target
786	K-th Smallest Prime Fraction
804	Unique Morse Code Words
814	Binary Tree Pruning
852	Peak Index in a Mountain Array
858	Mirror Reflection
867	Transpose Matrix
871	Minimum Number of Refueling Stops
890	Find and Replace Pattern
967	Numbers With Same Consecutive Differences
985	Sum of Even Numbers After Queries
987	Vertical Order Traversal of a Binary Tree
1020	Number of Enclaves
1048	Longest String Chain
1175	Prime Arrangements
1250	Check If It Is a Good Array
1254	Number of Closed Islands
1332	Remove Palindromic Subsequences
1337	The K Weakest Rows in a Matrix
1338	Reduce Array Size to The Half
1346	Check If N and Its Double Exist
1351	Count Negative Numbers in a Sorted Matrix
1385	Find the Distance Value Between Two Arrays
1423	Maximum Points You Can Obtain from Cards
1447	Simplified Fractions
1448	Count Good Nodes in Binary Tree
1480	Running Sum of 1d Array
1539	Kth Missing Positive Number
1608	Special Array With X Elements Greater Than or Equal X
1647	Minimum Deletions to Make Character Frequencies Unique
1680	Concatenation of Consecutive Binary Numbers
1689	Partitioning Into Minimum Number Of Deci-Binary Numbers
1710	Maximum Units on a Truck
1855	Maximum Distance Between a Pair of Values
2091	Removing Minimum and Maximum From Array
2147	Number of Ways to Divide a Long Corridor
2183	Count Array Pairs Divisible by K
2197	Replace Non-Coprime Numbers in Array
2280	Minimum Lines to Represent a Line Chart
2478	Number of Beautiful Partitions

Basic algorithm implementations

Binary indexed tree (Fenwick tree)

No.	Solutions where implemented	Lang	Notes
315	Count of Smaller Numbers After Self		Tree for counting numbers less than X

Binary search

No.	Solutions where implemented	Lang	Notes
34	Find First and Last Position of Element in Sorted Array		Search for leftmost and rightmost in series of equals
35	Search Insert Position		Search for leftmost
74	Search a 2D Matrix		Simple search with linear indexing of 2D matrix
240	Search a 2D Matrix II		Simple search
704	Binary Search		Simple search

Greatest common divisor (GCD)

No.	Solutions where implemented	Lang	Notes
1447	Simplified Fractions
2280	Minimum Lines to Represent a Line Chart

Single-linked list

No.	Solutions where implemented	Lang	Notes
25	Reverse Nodes in k-Group
92	Reverse Linked List II

Factorization

No.	Solutions where implemented	Lang	Notes
279	Perfect Squares		Simple factorization

Other helpers

Helper	Solution	Lang
Py implementation of ListNode’s __str__ and __repr__	25. Reverse Nodes in k-Group
Building TreeNode’s tree from array	623. Add One Row to Tree
Dynamic array	637. Average of Levels in Binary Tree
Swift queue using single-linked list	695. Max Area of Island
Building TreeNode’s tree from array	814. Binary Tree Pruning