Introduction

This repository contains a list of detailed posts and solutions for data structure and algorithm related problems.

Below is a table of LeetCode posts. The posts span from 05/2020 through present. Over this time frame the quality of the solutions gradually progress from novice (05/2020 - 08/2020) to intermediate (08/2020 - 11/2020) to expert (11/2020 - present).

The problem number links to the problem statement and the solution links to my discussion post / solution.

About 10% of the posts require a LeetCode membership to view, the rest do not.

This repository also contains a folder called old_practice_problems. The folder contains older solutions (02/2020) and my thought process approaching the problem for the first time.

Aside

The progression in quality of the posts below is closely linked to my progression in competitive programmimg (shown here) which can be compared to a larger population of programmers (shown here).

LeetCode Posts

Problem	Title and Solution	Solution Type
59	spiral matrix ii	Arrays
750	number of corner rectangles	Arrays
764	largest plus sign	Arrays
908	smallest range i	Arrays
922	sort array by parity ii	Arrays
1031	maximum sum of two non overlapping subarrays	Arrays
1385	find the distance value between two arrays	Arrays
1441	build an array with stack operations	Arrays
1292	maximum side length of a square with sum less than or equal to threshold	Arrays Binary Search
5	longest palindromic substring	Binary Search
275	h index ii	Binary Search
483	smallest good base	Binary Search
718	maximum length of repeated subarray	Binary Search
825	friends of appropriate ages	Binary Search
1095	find in mountain array	Binary Search
1283	find the smallest divisor given a threshold	Binary Search
1428	leftmost column with at least a one	Binary Search
1618	maximum font to fit a sentence in a screen	Binary Search
99	recover binary search tree	Binary Search Trees (BST)
510	inorder successor in bst ii	Binary Search Trees (BST)
1146	snapshot array	Binary Search Design Data Structure
508	most frequent subtree sum	Binary Trees
814	binary tree pruning	Binary Trees
1022	sum of root to leaf binary numbers	Binary Trees
1080	insufficient nodes in root to leaf paths	Binary Trees
1379	find a corresponding node of a binary tree in a clone of that tree	Binary Trees
1430	check if a string is a valid sequence from root to leaves path in a binary tree	Binary Trees
1318	minimum flips to make a or b equal to c	Bit Manipulation
568	maximum vacation days	Breadth First Search (BFS)
650	2 keys keyboard	Breadth First Search (BFS)
752	open the lock	Breadth First Search (BFS)
818	race car	Breadth First Search (BFS)
882	reachable nodes in subdivided graph	Breadth First Search (BFS)
1036	escape a large maze	Breadth First Search (BFS)
1145	binary tree coloring game	Breadth First Search (BFS)
1219	path with maximum gold	Breadth First Search (BFS)
1284	minimum number of flips to convert binary matrix to zero matrix	Breadth First Search (BFS)
1368	minimum cost to make at least one valid path in a grid	Breadth First Search (BFS)
1601	maximum number of achievable transfer requests	Breadth First Search (BFS)
1602	find nearest right node in binary tree	Breadth First Search (BFS)
1660	correct a binary tree	Breadth First Search (BFS)
1730	shortest path to get food	Breadth First Search (BFS)
504	base 7	Change of Base
51	n queens	Depth First Search (DFS)
698	partition to k equal sum subsets	Depth First Search (DFS)
1020	number of enclaves	Depth First Search (DFS) Breadth First Search (BFS)
641	design circular deque	Design Data Structure
933	number of recent calls	Design Data Structure
273	integer to english words	Divide and Conquer
70	climbing stairs	Dynamic Programming
375	guess number higher or lower ii	Dynamic Programming
377	combination sum iv	Dynamic Programming
464	can i win	Dynamic Programming
486	predict the winner	Dynamic Programming
494	target sum	Dynamic Programming
629	k inverse pairs array	Dynamic Programming
639	decode ways ii	Dynamic Programming
746	min cost climbing stairs	Dynamic Programming
801	minimum swaps to make sequences increasing	Dynamic Programming
813	largest sum of averages	Dynamic Programming
983	minimum cost for tickets	Dynamic Programming
1024	video stitching	Dynamic Programming
1025	divisor game	Dynamic Programming
1027	longest arithmetic subsequence	Dynamic Programming
1216	valid palindrome iii	Dynamic Programming
1235	maximum profit in job scheduling	Dynamic Programming
1307	verbal arithmetic puzzle	Dynamic Programming
1312	minimum insertion steps to make a string palindrome	Dynamic Programming
1690	stone game vii	Dynamic Programming
1692	count ways to distribute candies	Dynamic Programming
431	encode n ary tree to binary tree	Encoding and Decoding N-ary Trees Binary Trees
865	smallest subtree with all the deepest nodes	Eulerian Path
1650	lowest common ancestor of a binary tree iii	Eulerian Path
1676	lowest common ancestor of a binary tree iv	Eulerian Path
1740	find distance in a binary tree	Eulerian Path Visual Solutions
307	range sum query mutable	Fenwick Trees
683	k empty slots	Fenwick Trees
1606	find servers that handled most number of requests	Fenwick Trees
317	shortest distance from all buildings	Floyd-Warshall Breadth First Search (BFS)
348	design tic tac toe	Game Related
529	minesweeper	Game Related
909	snakes and ladders	Game Related
950	reveal cards in increasing order	Game Related
1210	minimum moves to reach target with rotations	Game Related Breadth First Search (BFS)
538	convert bst to greater tree	Greater Trees
765	couples holding hands	Greedy
995	minimum number of k consecutive bit flips	Greedy
1090	largest values from labels	Greedy
1686	stone game vi	Greedy
132	palindrome partitioning ii	Greedy Algorithm
1349	maximum students taking exam	Greedy Algorithm
1147	longest chunked palindrome decomposition	Greedy Double Ended Queues
296	best meeting point	Greedy Greedy Algorithm
727	minimum window subsequence	Greedy Greedy Algorithm
149	max points on a line	Hashing
893	groups of special equivalent strings	Hashing
871	minimum number of refueling stops	Heap
1696	jump game vi	Heap
1655	distribute repeating integers	Heap Breadth First Search (BFS)
798	smallest rotation with highest score	Interval Scheduling:
25	reverse nodes in k group	Linked-Lists
82	remove duplicates from sorted list ii	Linked-Lists
430	flatten a multilevel doubly linked list	Linked-Lists
708	insert into a sorted circular linked list	Linked-Lists
1290	convert binary number in a linked list to integer	Linked-Lists
1634	add two polynomials represented as linked lists	Linked-Lists
448	find all numbers disappeared in an array	Masks
864	shortest path to get all keys	Masks Breadth First Search (BFS)
526	beautiful arrangement	Masks Top Down DP
474	ones and zeroes	Memoization
308	range sum query 2d mutable	Memoization Fenwick Trees
423	reconstruct original digits from english	Multiset
1742	maximum number of balls in a box	Multiset
1745	palindrome partitioning iv	Multiset Prefix Sum Array
1623	all valid triplets that can represent a country	MySQL
1633	percentage of users attended a contest	MySQL
1667	fix names in a table	MySQL
1693	daily leads and partners	MySQL
1490	clone n ary tree	N-ary Trees
1506	find root of n ary tree	N-ary Trees
1600	throne inheritance	N-ary Trees
1257	smallest common region	N-ary Trees Lowest Common Ancestor
15	3sum	Other
32	longest valid parentheses	Other
118	pascals triangle	Other
248	strobogrammatic number iii	Other
268	missing number	Other
306	additive number	Other
350	intersection of two arrays ii	Other
396	rotate function	Other
760	find anagram mappings	Other
775	global and local inversions	Other
780	reaching points	Other
800	similar rgb color	Other
821	shortest distance to a character	Other
843	guess the word	Other
858	mirror reflection	Other
884	uncommon words from two sentences	Other
887	super egg drop	Other
1001	grid illumination	Other
1015	smallest integer divisible by k	Other
1054	distant barcodes	Other
1138	alphabet board path	Other
1217	minimum cost to move chips to the same position	Other
1253	reconstruct a 2 row binary matrix	Other
1266	minimum time visiting all points	Other
1291	sequential digits	Other
1360	number of days between two dates	Other
1455	check if a word occurs as a prefix of any word in a sentence	Other
1488	avoid flood in the city	Other
1503	last moment before all ants fall out of a plank	Other
1599	maximum profit of operating a centennial wheel	Other
1610	maximum number of visible points	Other
1653	minimum deletions to make string balanced	Other
1743	restore the array from adjacent pairs	Other
1386	cinema seat allocation	Other Greedy
399	evaluate division	Path Finding
573	squirrel simulation	Path Finding
18	4sum	Pointers
713	subarray product less than k	Pointers
334	increasing triplet subsequence	Prefix Sum Array
1714	sum of special evenly spaced elements in array	Prefix Sum Array
1744	can you eat your favorite candy on your favorite day	Prefix Sum Array
688	knight probability in chessboard	Probability
808	soup servings	Probability
1377	frog position after t seconds	Probability
616	add bold tag in string	Rabin-Karp
1316	distinct echo substrings	Rabin-Karp
773	sliding puzzle	Rabin-Karp Breadth First Search (BFS)
130	surrounded regions	Recursion
131	palindrome partitioning	Recursion
139	word break	Recursion
140	word break ii	Recursion
463	island perimeter	Recursion
906	super palindromes	Recursion
1088	confusing number ii	Recursion
1301	number of paths with max score	Recursion
1548	the most similar path in a graph	Recursion
1612	check if two expression trees are equivalent	Recursion Breadth First Search (BFS)
546	remove boxes	Recursion Memoization
1240	tiling a rectangle with the fewest squares	Recursion Simulation
732	my calendar iii	Scheduling:
1157	online majority element in subarray	Segment Tree
1673	find the most competitive subsequence	Segment Tree
1335	minimum difficulty of a job schedule	Segment Tree Dynamic Programming
794	valid tic tac toe state	Simulation Game Related
749	contain virus	Simulation Union-Find Visual Solutions
1206	design skiplist	Skip List
1100	find k length substrings with no repeated characters	Sliding Window
1708	largest subarray length k	Sliding Window
646	maximum length of pair chain	Sorting
757	set intersection size at least two	Sorting
1333	filter restaurants by vegan friendly price and distance	Sorting
1356	sort integers by the number of 1 bits	Sorting
220	contains duplicate iii	Sorting Double Ended Queues
20	valid parentheses	Stacks
71	simplify path	Stacks
85	maximal rectangle	Stacks
503	next greater element ii	Stacks
604	design compressed string iterator	Stacks
1598	crawler log folder	Stacks
1106	parsing a boolean expression	Stacks Parsing
188	best time to buy and sell stock iv	State Machines
265	paint house ii	State Machines
276	paint fence	State Machines
740	delete and earn	State Machines
161	one edit distance	String Manipulation
186	reverse words in a string ii	String Manipulation
395	longest substring with at least k repeating characters	String Manipulation
557	reverse words in a string iii	String Manipulation
811	subdomain visit count	String Manipulation
824	goat latin	String Manipulation
856	score of parentheses	String Manipulation
859	buddy strings	String Manipulation
1236	web crawler	String Manipulation
454	4sum ii	Sub-problem
1242	web crawler multithreaded	Threading: Breadth First Search (BFS)
312	burst balloons	Top Down DP
329	longest increasing path in a matrix	Top Down DP
337	house robber iii	Top Down DP
471	encode string with shortest length	Top Down DP
913	cat and mouse	Top Down DP
955	delete columns to make sorted ii	Top Down DP
956	tallest billboard	Top Down DP
1043	partition array for maximum sum	Top Down DP
1125	smallest sufficient team	Top Down DP
1340	jump game v	Top Down DP
1420	build array where you can find the maximum exactly k comparisons	Top Down DP
1449	form largest integer with digits that add up to target	Top Down DP
1473	paint house iii	Top Down DP
1659	maximize grid happiness	Top Down DP
1681	minimum incompatibility	Top Down DP
1682	longest palindromic subsequence ii	Top Down DP
1691	maximum height by stacking cuboids	Top Down DP
1728	cat and mouse ii	Top Down DP
1406	stone game iii	Top Down DP Game Related
164	maximum gap	Trie
745	prefix and suffix search	Trie
820	short encoding of words	Trie
1016	binary string with substrings representing 1 to n	Trie
1178	number of valid words for each puzzle	Trie
1233	remove sub folders from the filesystem	Trie
127	word ladder	Trie Breadth First Search (BFS)
1397	find all good strings	Trie Top Down DP
839	similar string groups	Trie Union-Find
80	remove duplicates from sorted array ii	Two-pointer
1287	element appearing more than 25 in sorted array	Two-pointer
1580	put boxes into the warehouse ii	Two-pointer
128	longest consecutive sequence	Union-Find
261	graph valid tree	Union-Find
305	number of islands ii	Union-Find
547	friend circles	Union-Find
711	number of distinct islands ii	Union-Find
721	accounts merge	Union-Find
737	sentence similarity ii	Union-Find
924	minimize malware spread	Union-Find
928	minimize malware spread ii	Union-Find
990	satisfiability of equality equations	Union-Find
1061	lexicographically smallest equivalent string	Union-Find
1101	the earliest moment when everyone become friends	Union-Find
1168	optimize water distribution in a village	Union-Find
1202	smallest string with swaps	Union-Find
1258	synonymous sentences	Union-Find
1319	number of operations to make network connected	Union-Find
1579	remove max number of edges to keep graph fully traversable	Union-Find
1627	graph connectivity with threshold	Union-Find
1632	rank transform of a matrix	Union-Find
1697	checking existence of edge length limited paths	Union-Find
352	data stream as disjoint intervals	Union-Find Binary Search
1434	number of ways to wear different hats to each other	Union-Find Top Down DP
959	regions cut by slashes	Union-Find Visual Solutions
172	factorial trailing zeroes	Visual Solutions
319	bulb switcher	Visual Solutions
498	diagonal traverse	Visual Solutions
790	domino and tromino tiling	Visual Solutions
963	minimum area rectangle ii	Visual Solutions
1351	count negative numbers in a sorted matrix	Visual Solutions
1644	lowest common ancestor of a binary tree ii	Visual Solutions Binary Trees Eulerian Path
1274	number of ships in a rectangle	Visual Solutions Divide and Conquer