The PythonWithSean 650

How To Use This List

Go in order by topic. Complete one topic before moving to the next.
Within each topic, do Easy first, then Medium, then Hard.
Time yourself: 15-20 min for Easy, 25-35 min for Medium, 40-50 min for Hard.
If stuck after the time limit, read the editorial, understand it, then redo the problem the next day without looking.
Track your progress. Print this page or keep a spreadsheet. Mark each problem as you complete it.

1. Arrays & Hashing (48)

#	Problem	Difficulty	Pattern
1	Two Sum	Easy	Hash Map
2	Contains Duplicate	Easy	Hash Set
3	Valid Anagram	Easy	Frequency Count
4	Concatenation of Array	Easy	Array Basics
5	Replace Elements with Greatest on Right	Easy	Right to Left
6	Is Subsequence	Easy	Two Pointers
7	Length of Last Word	Easy	String
8	Longest Common Prefix	Easy	String
9	Pascal's Triangle	Easy	Simulation
10	Remove Element	Easy	In-Place
11	Majority Element	Easy	Boyer-Moore
12	Roman to Integer	Easy	Hash Map
13	Missing Number	Easy	Math / XOR
14	Next Greater Element I	Easy	Stack + Map
15	Unique Email Addresses	Easy	String + Set
16	Remove Duplicates from Sorted Array	Easy	In-Place
17	Range Sum Query - Immutable	Easy	Prefix Sum
18	Group Anagrams	Medium	Hash Map
19	Top K Frequent Elements	Medium	Bucket Sort
20	Product of Array Except Self	Medium	Prefix/Suffix
21	Valid Sudoku	Medium	Hash Set
22	Encode and Decode Strings	Medium	Design
23	Longest Consecutive Sequence	Medium	Hash Set
24	Sort Colors	Medium	Dutch Flag
25	Subarray Sum Equals K	Medium	Prefix Sum + Map
26	Find All Anagrams in a String	Medium	Sliding Window
27	Determine if Two Strings Are Close	Medium	Frequency
28	Custom Sort String	Medium	Hash Map
29	Hand of Straights	Medium	Greedy + Map
30	Insert Delete GetRandom O(1)	Medium	Hash Map + Array
31	Repeated DNA Sequences	Medium	Hash Set
32	Integer to Roman	Medium	Greedy
33	Rotate Array	Medium	Reverse Trick
34	Brick Wall	Medium	Hash Map
35	Push Dominoes	Medium	Two Pointers
36	Remove Duplicates from Sorted Array II	Medium	In-Place
37	Best Time to Buy and Sell Stock II	Medium	Greedy
38	Spiral Matrix	Medium	Simulation
39	Set Matrix Zeroes	Medium	In-Place
40	Game of Life	Medium	Simulation
41	H-Index	Medium	Sorting / Counting
42	Range Sum Query 2D	Medium	Prefix Sum 2D
43	Min Swaps for Balanced String	Medium	Greedy
44	Spiral Matrix II	Medium	Simulation
45	Contiguous Array	Medium	Prefix Sum + Map
46	First Missing Positive	Hard	Index as Hash
47	Naming a Company	Hard	Hash Set
48	Text Justification	Hard	Simulation

2. Two Pointers (25)

#	Problem	Difficulty	Pattern
49	Valid Palindrome	Easy	Two Pointers
50	Two Sum II	Medium	Two Pointers
51	3Sum	Medium	Sort + Two Ptr
52	Container With Most Water	Medium	Two Pointers
53	Move Zeroes	Easy	Two Pointers
54	Merge Sorted Array	Easy	Two Pointers
55	Reverse String	Easy	Two Pointers
56	Squares of a Sorted Array	Easy	Two Pointers
57	Assign Cookies	Easy	Greedy + Sort
58	Backspace String Compare	Easy	Two Pointers
59	Intersection of Two Arrays II	Easy	Hash Map
60	3Sum Closest	Medium	Sort + Two Ptr
61	Boats to Save People	Medium	Sort + Two Ptr
62	Partition Labels	Medium	Greedy
63	4Sum	Medium	Sort + Two Ptr
64	Sort Array By Parity	Easy	Two Pointers
65	Longest Word in Dict by Deleting	Medium	Two Pointers
66	Min Diff Between K Scores	Easy	Sort + Window
67	Two Sum IV - BST	Easy	BST + Set
68	Subsequences with Sum Condition	Medium	Sort + Two Ptr
69	Bag of Tokens	Medium	Sort + Two Ptr
70	String Compression	Medium	Two Pointers
71	4Sum II	Medium	Hash Map
72	Trapping Rain Water	Hard	Two Pointers
73	Shortest Unsorted Subarray	Medium	Two Pointers

3. Sliding Window (22)

#	Problem	Difficulty	Pattern
74	Best Time to Buy and Sell Stock	Easy	Sliding Window
75	Contains Duplicate II	Easy	Hash Set Window
76	Longest Substring Without Repeating Chars	Medium	Sliding Window
77	Longest Repeating Char Replacement	Medium	Sliding Window
78	Permutation in String	Medium	Sliding Window
79	Minimum Size Subarray Sum	Medium	Sliding Window
80	Fruit Into Baskets	Medium	Sliding Window
81	Max Vowels in Substring	Medium	Fixed Window
82	Grumpy Bookstore Owner	Medium	Fixed Window
83	Max Consecutive Ones III	Medium	Sliding Window
84	Equal Substrings Within Budget	Medium	Sliding Window
85	Count Nice Subarrays	Medium	Sliding Window
86	Binary Subarrays With Sum	Medium	Prefix Sum / Window
87	Frequency of Most Frequent Element	Medium	Sort + Window
88	Max Points from Cards	Medium	Sliding Window
89	Maximum Erasure Value	Medium	Sliding Window
90	Min Flips for Alternating String	Medium	Sliding Window
91	Minimum Window Substring	Hard	Sliding Window
92	Sliding Window Maximum	Hard	Monotonic Deque
93	Substring with Concat of All Words	Hard	Sliding Window
94	Subarrays with K Different Integers	Hard	Sliding Window
95	Count Subarrays Max Appears K Times	Medium	Sliding Window

4. Stack (28)

#	Problem	Difficulty	Pattern
96	Valid Parentheses	Easy	Stack
97	Implement Queue using Stacks	Easy	Stack
98	Implement Stack using Queues	Easy	Queue
99	Baseball Game	Easy	Stack
100	Min Stack	Medium	Stack Design
101	Evaluate Reverse Polish Notation	Medium	Stack
102	Daily Temperatures	Medium	Monotonic Stack
103	Car Fleet	Medium	Stack + Sort
104	Asteroid Collision	Medium	Stack
105	Decode String	Medium	Stack
106	Removing Stars From a String	Medium	Stack
107	Online Stock Span	Medium	Monotonic Stack
108	132 Pattern	Medium	Monotonic Stack
109	Simplify Path	Medium	Stack
110	Remove Adjacent Duplicates II	Medium	Stack
111	Remove K Digits	Medium	Monotonic Stack
112	Validate Stack Sequences	Medium	Stack Simulation
113	Flatten Nested List Iterator	Medium	Stack
114	Basic Calculator II	Medium	Stack
115	Next Greater Element II	Medium	Monotonic Stack
116	Sum of Subarray Minimums	Medium	Monotonic Stack
117	Sum of Subarray Ranges	Medium	Monotonic Stack
118	Largest Rectangle in Histogram	Hard	Monotonic Stack
119	Maximal Rectangle	Hard	Stack + DP
120	Basic Calculator	Hard	Stack + Recursion
121	Longest Valid Parentheses	Hard	Stack / DP
122	Maximum Frequency Stack	Hard	Stack + Map
123	Visible People in Queue	Hard	Monotonic Stack

5. Binary Search (28)

#	Problem	Difficulty	Pattern
124	Binary Search	Easy	Binary Search
125	Search Insert Position	Easy	Binary Search
126	Guess Number Higher or Lower	Easy	Binary Search
127	First Bad Version	Easy	Binary Search
128	Valid Perfect Square	Easy	Binary Search
129	Sqrt(x)	Easy	Binary Search
130	Arranging Coins	Easy	Binary Search
131	Search a 2D Matrix	Medium	Binary Search
132	Koko Eating Bananas	Medium	BS on Answer
133	Find Min in Rotated Sorted Array	Medium	Binary Search
134	Search in Rotated Sorted Array	Medium	Binary Search
135	Time Based Key-Value Store	Medium	Binary Search
136	Find Peak Element	Medium	Binary Search
137	First and Last Position	Medium	Binary Search
138	Search a 2D Matrix II	Medium	Binary Search
139	Ship Packages in D Days	Medium	BS on Answer
140	Single Element in Sorted Array	Medium	Binary Search
141	Spells and Potions	Medium	Sort + BS
142	Magnetic Force Between Balls	Medium	BS on Answer
143	Min Days for m Bouquets	Medium	BS on Answer
144	Peak Index in Mountain Array	Medium	Binary Search
145	Search in Rotated Array II	Medium	Binary Search
146	Kth Smallest in Sorted Matrix	Medium	Binary Search
147	Median of Two Sorted Arrays	Hard	Binary Search
148	Split Array Largest Sum	Hard	BS on Answer
149	Find in Mountain Array	Hard	Binary Search
150	Count Smaller After Self	Hard	Merge Sort / BIT
151	Count of Range Sum	Hard	Merge Sort / BS

6. Linked List (24)

#	Problem	Difficulty	Pattern
152	Reverse Linked List	Easy	Reversal
153	Merge Two Sorted Lists	Easy	Two Pointers
154	Linked List Cycle	Easy	Fast/Slow
155	Palindrome Linked List	Easy	Fast/Slow + Reverse
156	Remove Linked List Elements	Easy	Dummy Node
157	Intersection of Two Lists	Easy	Two Pointers
158	Middle of the Linked List	Easy	Fast/Slow
159	Reorder List	Medium	Fast/Slow + Reverse
160	Remove Nth Node From End	Medium	Two Pointers
161	Add Two Numbers	Medium	Math + LL
162	Copy List with Random Pointer	Medium	Hash Map
163	LRU Cache	Medium	DLL + Hash Map
164	Swap Nodes in Pairs	Medium	Pointer Manipulation
165	Sort List	Medium	Merge Sort
166	Partition List	Medium	Two Lists
167	Linked List Cycle II	Medium	Fast/Slow
168	Delete Middle Node	Medium	Fast/Slow
169	Odd Even Linked List	Medium	Pointer Manipulation
170	Add Two Numbers II	Medium	Stack + LL
171	Rotate List	Medium	Cycle + Count
172	Remove Duplicates II	Medium	Dummy Node
173	Flatten Multilevel DLL	Medium	DFS / Stack
174	Merge k Sorted Lists	Hard	Heap / Divide & Conquer
175	Reverse Nodes in k-Group	Hard	Reversal

7. Trees (42)

#	Problem	Difficulty	Pattern
176	Invert Binary Tree	Easy	DFS
177	Maximum Depth of Binary Tree	Easy	DFS
178	Same Tree	Easy	DFS
179	Subtree of Another Tree	Easy	DFS
180	Diameter of Binary Tree	Easy	DFS
181	Balanced Binary Tree	Easy	DFS
182	Path Sum	Easy	DFS
183	Symmetric Tree	Easy	DFS / BFS
184	Minimum Depth of Binary Tree	Easy	BFS
185	Sorted Array to BST	Easy	Divide & Conquer
186	Binary Tree Inorder Traversal	Easy	DFS
187	Binary Tree Preorder Traversal	Easy	DFS
188	Count Good Nodes	Medium	DFS
189	Level Order Traversal	Medium	BFS
190	Right Side View	Medium	BFS
191	Validate BST	Medium	DFS + Bounds
192	Kth Smallest in BST	Medium	Inorder
193	Build Tree from Preorder + Inorder	Medium	Divide & Conquer
194	LCA of Binary Tree	Medium	DFS
195	LCA of BST	Medium	BST Property
196	Zigzag Level Order	Medium	BFS
197	Path Sum II	Medium	DFS + Backtrack
198	Path Sum III	Medium	Prefix Sum + DFS
199	Sum Root to Leaf Numbers	Medium	DFS
200	BST Iterator	Medium	Stack + Inorder
201	Next Right Pointers	Medium	BFS
202	House Robber III	Medium	DFS + DP
203	All Nodes Distance K	Medium	BFS + Parent Map
204	Flatten Tree to LL	Medium	DFS
205	Max Width of Binary Tree	Medium	BFS + Indexing
206	Time for Tree to Be Infected	Medium	BFS + Parent Map
207	Delete Node in BST	Medium	BST Operations
208	Trim a BST	Medium	DFS
209	Unique BSTs	Medium	DP (Catalan)
210	Count Complete Tree Nodes	Medium	Binary Search
211	Recover BST	Medium	Inorder
212	Build from Inorder + Postorder	Medium	Divide & Conquer
213	Binary Tree Max Path Sum	Hard	DFS
214	Serialize and Deserialize Tree	Hard	BFS / DFS
215	Vertical Order Traversal	Hard	BFS + Sort
216	Binary Tree Cameras	Hard	Greedy DFS
217	Maximum Sum BST	Hard	DFS

8. Tries (10)

#	Problem	Difficulty	Pattern
218	Implement Trie	Medium	Trie
219	Add and Search Words	Medium	Trie + DFS
220	Replace Words	Medium	Trie
221	Map Sum Pairs	Medium	Trie
222	Longest Word in Dictionary	Medium	Trie + DFS
223	Search Suggestions System	Medium	Trie + Sort
224	Max XOR of Two Numbers	Medium	Bitwise Trie
225	Word Search II	Hard	Trie + Backtrack
226	Palindrome Pairs	Hard	Trie
227	Stream of Characters	Hard	Reverse Trie

9. Heap / Priority Queue (22)

#	Problem	Difficulty	Pattern
228	Kth Largest in Stream	Easy	Min Heap
229	Last Stone Weight	Easy	Max Heap
230	Kth Largest in Array	Medium	Quickselect / Heap
231	K Closest Points	Medium	Heap
232	Task Scheduler	Medium	Heap + Queue
233	Design Twitter	Medium	Heap + Design
234	Reorganize String	Medium	Heap
235	K Pairs with Smallest Sums	Medium	Heap
236	Seat Reservation Manager	Medium	Min Heap
237	Smallest in Infinite Set	Medium	Heap + Set
238	Max Subsequence Score	Medium	Sort + Heap
239	Total Cost to Hire K Workers	Medium	Two Heaps
240	Top K Frequent Words	Medium	Heap
241	Sort Chars by Frequency	Medium	Heap / Bucket
242	Ugly Number II	Medium	Heap / DP
243	IPO	Hard	Two Heaps
244	Find Median from Data Stream	Hard	Two Heaps
245	Sliding Window Median	Hard	Two Heaps
246	Smallest Range from K Lists	Hard	Heap
247	Trapping Rain Water II	Hard	Heap + BFS
248	Process Tasks Using Servers	Medium	Two Heaps
249	Super Ugly Number	Medium	Heap

10. Backtracking (22)

#	Problem	Difficulty	Pattern
250	Subsets	Medium	Backtracking
251	Combination Sum	Medium	Backtracking
252	Permutations	Medium	Backtracking
253	Subsets II	Medium	Backtracking + Skip
254	Combination Sum II	Medium	Backtracking + Skip
255	Permutations II	Medium	Backtracking + Skip
256	Word Search	Medium	DFS + Backtrack
257	Palindrome Partitioning	Medium	Backtracking
258	Letter Combos of Phone Number	Medium	Backtracking
259	Combinations	Medium	Backtracking
260	Generate Parentheses	Medium	Backtracking
261	Restore IP Addresses	Medium	Backtracking
262	Find Unique Binary String	Medium	Backtracking
263	Max Concat String Unique Chars	Medium	Backtracking
264	Partition to K Equal Subsets	Medium	Backtracking
265	Matchsticks to Square	Medium	Backtracking
266	Split String Descending	Medium	Backtracking
267	N-Queens	Hard	Backtracking
268	N-Queens II	Hard	Backtracking
269	Sudoku Solver	Hard	Backtracking
270	Expression Add Operators	Hard	Backtracking
271	Word Break II	Hard	Backtracking + Memo

11. Graphs (38)

#	Problem	Difficulty	Pattern
272	Number of Islands	Medium	DFS / BFS
273	Clone Graph	Medium	DFS + Map
274	Max Area of Island	Medium	DFS
275	Pacific Atlantic Water Flow	Medium	DFS
276	Surrounded Regions	Medium	DFS from Border
277	Rotting Oranges	Medium	Multi-source BFS
278	Course Schedule	Medium	Topological Sort
279	Course Schedule II	Medium	Topological Sort
280	Redundant Connection	Medium	Union Find
281	Accounts Merge	Medium	Union Find / DFS
282	Is Graph Bipartite?	Medium	BFS / DFS Coloring
283	Shortest Path in Binary Matrix	Medium	BFS
284	Open the Lock	Medium	BFS
285	Minimum Height Trees	Medium	Topological (Leaf Trim)
286	Cheapest Flights K Stops	Medium	Bellman-Ford / BFS
287	Network Delay Time	Medium	Dijkstra
288	Min Cost Connect Points	Medium	Prim / Kruskal
289	Snakes and Ladders	Medium	BFS
290	Evaluate Division	Medium	DFS / Union Find
291	Reorder Routes to City Zero	Medium	DFS
292	Find Eventual Safe States	Medium	DFS Cycle Detection
293	Shortest Bridge	Medium	DFS + BFS
294	Detonate Max Bombs	Medium	DFS / BFS
295	Keys and Rooms	Medium	DFS
296	Number of Provinces	Medium	DFS / Union Find
297	Find the Town Judge	Easy	Degree Count
298	All Paths Source to Target	Medium	DFS / Backtrack
299	Min Vertices to Reach All	Medium	Indegree
300	Possible Bipartition	Medium	BFS Coloring
301	Word Ladder	Hard	BFS
302	Swim in Rising Water	Hard	Dijkstra / BS + BFS
303	Alien Dictionary	Hard	Topological Sort
304	Reconstruct Itinerary	Hard	Euler Path DFS
305	Word Ladder II	Hard	BFS + Backtrack
306	Bus Routes	Hard	BFS
307	Critical Connections	Hard	Tarjan's Bridge
308	Longest Increasing Path	Hard	DFS + Memo
309	Making a Large Island	Hard	DFS + Union

12. 1D Dynamic Programming (38)

#	Problem	Difficulty	Pattern
310	Climbing Stairs	Easy	Fibonacci-style
311	Min Cost Climbing Stairs	Easy	DP
312	Fibonacci Number	Easy	DP / Math
313	N-th Tribonacci Number	Easy	DP
314	House Robber	Medium	DP
315	House Robber II	Medium	Circular DP
316	Longest Palindromic Substring	Medium	Expand Center / DP
317	Palindromic Substrings	Medium	Expand Center
318	Decode Ways	Medium	DP
319	Coin Change	Medium	DP (Unbounded)
320	Max Product Subarray	Medium	DP (min/max)
321	Word Break	Medium	DP + Set
322	Longest Increasing Subsequence	Medium	DP / Binary Search
323	Partition Equal Subset Sum	Medium	0/1 Knapsack
324	Maximum Subarray	Medium	Kadane's
325	Jump Game	Medium	Greedy / DP
326	Jump Game II	Medium	Greedy / DP
327	Perfect Squares	Medium	DP
328	Integer Break	Medium	DP / Math
329	Combination Sum IV	Medium	DP
330	Delete and Earn	Medium	DP (House Robber)
331	Buy Stock with Cooldown	Medium	State Machine DP
332	Minimum Cost for Tickets	Medium	DP
333	Longest Arithmetic Subsequence	Medium	DP + Map
334	Count Ways Good Strings	Medium	DP
335	Domino and Tromino Tiling	Medium	DP
336	Solving Questions Brainpower	Medium	DP
337	Arithmetic Slices	Medium	DP
338	Longest Turbulent Subarray	Medium	DP
339	Target Sum	Medium	DP (Subset Sum)
340	Extra Characters in String	Medium	DP + Set
341	Longest Palindromic Subsequence	Medium	DP
342	Max Length Pair Chain	Medium	DP / Greedy
343	Number of LIS	Medium	DP
344	Wiggle Subsequence	Medium	DP / Greedy
345	Longest Ideal Subsequence	Medium	DP
346	Ones and Zeroes	Medium	Knapsack DP
347	Max Points with Cost	Medium	DP

13. 2D Dynamic Programming (22)

#	Problem	Difficulty	Pattern
348	Unique Paths	Medium	Grid DP
349	Unique Paths II	Medium	Grid DP
350	Longest Common Subsequence	Medium	2D DP
351	Buy Stock with Fee	Medium	State Machine DP
352	Minimum Path Sum	Medium	Grid DP
353	Triangle	Medium	Grid DP
354	Maximal Square	Medium	2D DP
355	Coin Change II	Medium	Unbounded Knapsack
356	Interleaving String	Medium	2D DP
357	Stone Game	Medium	Interval DP
358	Stone Game II	Medium	Game DP
359	Last Stone Weight II	Medium	Knapsack
360	Edit Distance	Medium	2D DP
361	Regular Expression Matching	Hard	2D DP
362	Wildcard Matching	Hard	2D DP
363	Burst Balloons	Hard	Interval DP
364	Distinct Subsequences	Hard	2D DP
365	Stone Game III	Hard	Game DP
366	Profitable Schemes	Hard	3D Knapsack
367	Dungeon Game	Hard	Reverse Grid DP
368	Cherry Pickup	Hard	3D DP
369	Cherry Pickup II	Hard	3D DP

14. Greedy (28)

#	Problem	Difficulty	Pattern
370	Lemonade Change	Easy	Greedy
371	Max Units on a Truck	Easy	Sort + Greedy
372	Array Partition	Easy	Sort + Greedy
373	Gas Station	Medium	Greedy
374	Non-overlapping Intervals	Medium	Sort + Greedy
375	Min Arrows to Burst Balloons	Medium	Sort + Greedy
376	Queue Reconstruction by Height	Medium	Sort + Greedy
377	Min Deletions Unique Frequencies	Medium	Greedy
378	Reduce Array Size to Half	Medium	Greedy
379	Longest Happy String	Medium	Greedy + Heap
380	Advantage Shuffle	Medium	Sort + Greedy
381	Min Rounds All Tasks	Medium	Greedy + Math
382	Max Ice Cream Bars	Medium	Sort + Greedy
383	Dota2 Senate	Medium	Greedy + Queue
384	Two City Scheduling	Medium	Sort + Greedy
385	Video Stitching	Medium	Greedy
386	Largest Number	Medium	Custom Sort
387	Broken Calculator	Medium	Reverse Greedy
388	Minimize Maximum of Array	Medium	Greedy / BS
389	Max Length Positive Product	Medium	Greedy / DP
390	Flower Planting	Medium	Greedy + Graph
391	Candy	Hard	Two-Pass Greedy
392	Min Refueling Stops	Hard	Greedy + Heap
393	Earliest Day Full Bloom	Hard	Sort + Greedy
394	Min Cost Equal Array	Hard	Weighted Median
395	Max Events Attended	Medium	Greedy + Heap
396	Min Ops Array Continuous	Hard	Sort + Sliding Window
397	Max Points Archery	Medium	Bitmask / Greedy

15. Intervals (14)

#	Problem	Difficulty	Pattern
398	Summary Ranges	Easy	Intervals
399	Merge Intervals	Medium	Sort + Merge
400	Insert Interval	Medium	Intervals
401	Interval List Intersections	Medium	Two Pointers
402	Remove Covered Intervals	Medium	Sort + Greedy
403	My Calendar I	Medium	Binary Search / Sort
404	My Calendar II	Medium	Sweep Line
405	Car Pooling	Medium	Sweep Line
406	Meeting Rooms	Easy	Sort + Check
407	Meeting Rooms II	Medium	Sweep Line / Heap
408	Min Interval for Queries	Hard	Sort + Heap
409	Data Stream Disjoint Intervals	Hard	TreeMap / Sort
410	Employee Free Time	Hard	Merge + Sort
411	Range Module	Hard	Segment Tree / Sort

16. Math & Geometry (28)

#	Problem	Difficulty	Pattern
412	Plus One	Easy	Math
413	Happy Number	Easy	Fast/Slow Pointers
414	Palindrome Number	Easy	Math
415	Fizz Buzz	Easy	Modulo
416	Power of Two	Easy	Bit / Math
417	Power of Three	Easy	Math
418	Add Binary	Easy	Math
419	Ugly Number	Easy	Math
420	Excel Sheet Column Number	Easy	Base Conversion
421	Excel Sheet Column Title	Easy	Base Conversion
422	Set Mismatch	Easy	Math / Hash
423	GCD of Strings	Easy	GCD / Math
424	Rotate Image	Medium	Matrix Rotation
425	Count Primes	Medium	Sieve
426	Factorial Trailing Zeroes	Medium	Math
427	Multiply Strings	Medium	Math
428	Detect Squares	Medium	Hash Map + Geometry
429	Pow(x, n)	Medium	Fast Exponentiation
430	Reverse Integer	Medium	Math
431	Robot Bounded in Circle	Medium	Simulation
432	Random Pick with Weight	Medium	Prefix Sum + BS
433	Min Moves Equal Elements	Medium	Math
434	Min Moves Equal Elements II	Medium	Median
435	Angle Between Clock Hands	Medium	Math
436	Water and Jug Problem	Medium	GCD / BFS
437	Max Points on a Line	Hard	Hash Map + Math
438	Permutation Sequence	Hard	Math (Factorial)
439	Integer to English Words	Hard	Recursion

17. Bit Manipulation (18)

#	Problem	Difficulty	Pattern
440	Single Number	Easy	XOR
441	Number of 1 Bits	Easy	Bit Count
442	Counting Bits	Easy	DP + Bits
443	Reverse Bits	Easy	Bit Manipulation
444	Hamming Distance	Easy	XOR + Count
445	Complement of Base 10	Easy	Bit Flip
446	Sum of Two Integers	Medium	Bit Manipulation
447	Single Number II	Medium	Bit Counting
448	Single Number III	Medium	XOR + Partition
449	Bitwise AND of Range	Medium	Bit Shift
450	Find the Duplicate Number	Medium	Fast/Slow / Bits
451	UTF-8 Validation	Medium	Bit Masking
452	Min Flips a OR b = c	Medium	Bit Manipulation
453	XOR Queries of Subarray	Medium	Prefix XOR
454	Total Hamming Distance	Medium	Bit Count
455	Gray Code	Medium	Bit Manipulation
456	Divide Two Integers	Medium	Bit Shift
457	Decode XORed Permutation	Medium	XOR

18. Union Find (12)

#	Problem	Difficulty	Pattern
458	Longest Consecutive Sequence	Medium	Union Find / Set
459	Connected Components	Medium	Union Find
460	Graph Valid Tree	Medium	Union Find
461	Most Stones Removed	Medium	Union Find
462	Satisfiability of Equality	Medium	Union Find
463	Network Connected	Medium	Union Find
464	Smallest String with Swaps	Medium	Union Find + Sort
465	Similar String Groups	Hard	Union Find
466	Number of Islands II	Hard	Union Find
467	Couples Holding Hands	Hard	Union Find / Greedy
468	Minimize Malware Spread	Hard	Union Find
469	Regions Cut By Slashes	Medium	Union Find

19. Design (14)

#	Problem	Difficulty	Pattern
470	Design HashMap	Easy	Hash Map
471	Design HashSet	Easy	Hash Set
472	Min Stack	Medium	Stack Design
473	LRU Cache	Medium	DLL + Map
474	Design Browser History	Medium	Stack / DLL
475	Implement Trie	Medium	Trie
476	Design Circular Queue	Medium	Array / LL
477	Design Underground System	Medium	Hash Map
478	Snapshot Array	Medium	Binary Search
479	Online Stock Span	Medium	Monotonic Stack
480	LFU Cache	Hard	DLL + Map
481	Find Median from Stream	Hard	Two Heaps
482	Autocomplete System	Hard	Trie + Sort
483	All O(1) Data Structure	Hard	DLL + Map

20. String (30)

#	Problem	Difficulty	Pattern
484	Valid Palindrome II	Easy	Two Pointers
485	First Unique Character	Easy	Hash Map
486	Reverse Words in String	Medium	String
487	Zigzag Conversion	Medium	Simulation
488	String to Integer (atoi)	Medium	Parsing
489	Count and Say	Medium	Simulation
490	Compare Version Numbers	Medium	String Split
491	Longest Palindrome	Easy	Frequency Count
492	Repeated Substring Pattern	Easy	String
493	Isomorphic Strings	Easy	Hash Map
494	Word Pattern	Easy	Hash Map
495	Ransom Note	Easy	Frequency Count
496	Implement strStr()	Easy	String Match
497	Min Remove Valid Parens	Medium	Stack / Two Pass
498	Longest Substr K Repeating	Medium	Divide & Conquer
499	Optimal Partition of String	Medium	Greedy + Set
500	Group Anagrams	Medium	Hash Map
501	String Compression	Medium	Two Pointers
502	Basic Calculator II	Medium	Stack + Parse
503	Remove Adjacent Duplicates	Easy	Stack
504	Min Penalty for a Shop	Medium	Prefix Sum
505	Bulls and Cows	Medium	Hash Map
506	Number of Atoms	Hard	Stack + Parse
507	Shortest Palindrome	Hard	KMP / Rolling Hash
508	Minimum Window Substring	Hard	Sliding Window
509	Distinct Subsequences	Hard	DP
510	Count Unique Chars Substrings	Hard	Math
511	Palindrome Partitioning II	Hard	DP
512	Minimum Window Substring	Hard	Sliding Window
513	Reorganize String	Medium	Heap / Greedy

21. Sorting (15)

#	Problem	Difficulty	Pattern
514	Merge Sorted Array	Easy	Two Pointers
515	Valid Anagram	Easy	Sort / Hash
516	Sort an Array	Medium	Merge Sort
517	Sort List	Medium	Merge Sort
518	Insertion Sort List	Medium	Insertion Sort
519	Kth Largest Element	Medium	Quickselect
520	Wiggle Sort II	Medium	Sort + Place
521	Largest Number	Medium	Custom Comparator
522	Top K Frequent	Medium	Bucket Sort
523	Sort Chars by Frequency	Medium	Bucket Sort
524	Relative Sort Array	Easy	Counting Sort
525	Maximum Gap	Medium	Radix / Bucket Sort
526	Sort Colors	Medium	Dutch Flag
527	Pancake Sorting	Medium	Simulation
528	Count Smaller After Self	Hard	Merge Sort

22. Prefix Sum (14)

#	Problem	Difficulty	Pattern
529	Running Sum of 1D Array	Easy	Prefix Sum
530	Find Pivot Index	Easy	Prefix Sum
531	Range Sum Query Immutable	Easy	Prefix Sum
532	Subarray Sum Equals K	Medium	Prefix Sum + Map
533	Contiguous Array	Medium	Prefix Sum + Map
534	Product Except Self	Medium	Prefix / Suffix
535	Random Pick with Weight	Medium	Prefix Sum + BS
536	Range Sum Query 2D	Medium	2D Prefix Sum
537	Min Penalty for Shop	Medium	Prefix Sum
538	Path Sum III	Medium	Prefix Sum + DFS
539	XOR Queries	Medium	Prefix XOR
540	Ways to Split Array	Medium	Prefix Sum
541	Max Sum Almost Unique Subarray	Medium	Window + Prefix
542	Count Subarrays Fixed Bounds	Hard	Sliding Window

23. Matrix (15)

#	Problem	Difficulty	Pattern
543	Reshape the Matrix	Easy	Matrix
544	Transpose Matrix	Easy	Matrix
545	Matrix Diagonal Sum	Easy	Matrix
546	Rotate Image	Medium	Matrix Rotation
547	Spiral Matrix	Medium	Simulation
548	Set Matrix Zeroes	Medium	In-Place
549	Where Will Ball Fall	Medium	Simulation
550	01 Matrix	Medium	BFS
551	Diagonal Traverse	Medium	Simulation
552	Toeplitz Matrix	Easy	Matrix
553	Number of Islands	Medium	DFS / BFS
554	Surrounded Regions	Medium	DFS from Border
555	Word Search	Medium	DFS + Backtrack
556	Maximal Square	Medium	DP
557	Shortest Path Binary Matrix	Medium	BFS

24. Recursion (12)

#	Problem	Difficulty	Pattern
558	Power of Two	Easy	Recursion
559	Power of Four	Easy	Recursion / Math
560	Reverse Linked List	Easy	Recursion
561	Swap Nodes in Pairs	Medium	Recursion
562	Merge Two Sorted Lists	Easy	Recursion
563	Pow(x, n)	Medium	Recursion (D&C)
564	Generate Parentheses	Medium	Recursion
565	Different Ways to Add Parens	Medium	Divide & Conquer
566	Kth Symbol in Grammar	Medium	Recursion
567	Predict the Winner	Medium	Game Recursion
568	Sort List	Medium	Merge Sort Recursion
569	Strobogrammatic Number II	Medium	Recursion

25. Mixed Hard Problems (41)

These are the problems that test everything you've learned. Complete these and you're elite.

#	Problem	Difficulty	Pattern
570	LRU Cache	Medium	Design
571	Design Circular Deque	Medium	Design
572	Design Linked List	Medium	Linked List
573	Implement Stack using Queues	Easy	Design
574	Maximal Network Rank	Medium	Graph
575	Minimum Genetic Mutation	Medium	BFS
576	Jump Game III	Medium	BFS / DFS
577	Jump Game IV	Hard	BFS
578	Max Profit Job Scheduling	Hard	DP + BS
579	Largest Color Value	Hard	Topo Sort + DP
580	Min Cost K Workers	Hard	Sort + Heap
581	Count Vowels Permutation	Hard	DP
582	Frog Jump	Hard	DP + Set
583	Strange Printer	Hard	Interval DP
584	Min Window Subsequence	Hard	Two Pointers / DP
585	Concatenated Words	Hard	DP + Trie
586	Count Pickup Delivery	Hard	Math / DP
587	Design Graph Shortest Path	Hard	Dijkstra
588	Ways to Arrive at Destination	Medium	Dijkstra + DP
589	Longest String Chain	Medium	DP + Map
590	Min Ops Reduce X to Zero	Medium	Sliding Window / Prefix
591	Where Will Ball Fall	Medium	Simulation
592	Number of Enclaves	Medium	DFS / BFS
593	Count Good Meals	Medium	Hash Map
594	Find All Farmland	Medium	DFS / BFS
595	Stamping the Sequence	Hard	Greedy (Reverse)
596	Count of Range Sum	Hard	Merge Sort
597	Increasing Paths in Grid	Hard	DFS + Memo
598	Min Obstacle Removal	Hard	0-1 BFS
599	Maximize Score N Ops	Hard	Bitmask DP
600	Min Days Disconnect Island	Hard	Articulation Points
601	Count Subarrays Median K	Hard	Hash Map
602	Amount Painted Each Day	Hard	Sweep Line
603	Min Cost Connect Sticks	Medium	Heap
604	Next Permutation	Medium	Math
605	Can Place Flowers	Easy	Greedy
606	Kids With Greatest Candies	Easy	Array
607	Number of Recent Calls	Easy	Queue
608	Asteroid Collision	Medium	Stack
609	Find Highest Altitude	Easy	Prefix Sum
610	Equal Row & Column Pairs	Medium	Hash Map
611	Find K Closest Elements	Medium	Binary Search
612	Last Day Still Cross	Hard	BS + BFS / UF
613	Number of Good Paths	Hard	Union Find + Sort
614	Shortest Path All Nodes	Hard	BFS + Bitmask
615	Smallest Sufficient Team	Hard	Bitmask DP
616	Number of Music Playlists	Hard	DP
617	Tallest Billboard	Hard	DP
618	Count Palindromic Subseqs	Hard	DP
619	Min Cost Cut Stick	Hard	Interval DP
620	Max Running Time N Computers	Hard	BS + Greedy
621	Min Taps Water Garden	Hard	Greedy
622	Parallel Courses III	Hard	Topo Sort + DP
623	Min Time Collect Apples	Medium	DFS
624	Online Election	Medium	BS + Precompute
625	My Calendar III	Hard	Sweep Line
626	Flowers in Full Bloom	Hard	Sort + BS
627	Path with Min Effort	Medium	Dijkstra / BS+BFS
628	Critical MST Edges	Hard	Kruskal + UF
629	Dice Rolls Target Sum	Medium	DP
630	Min Falling Path Sum	Medium	DP
631	Number of Closed Islands	Medium	DFS / BFS
632	Min Score Path	Medium	BFS / UF
633	Constrained Subsequence Sum	Hard	DP + Deque
634	Restore the Array	Hard	DP
635	Sum of Distances in Tree	Hard	Rerooting DP
636	Max Profit Job Scheduling	Hard	DP + BS
637	Largest Color Value	Hard	Topo Sort + DP
638	Count Vowels Permutation	Hard	DP
639	Frog Jump	Hard	DP + Set
640	Strange Printer	Hard	Interval DP
641	Concatenated Words	Hard	DP + Trie
642	Min Cost K Workers	Hard	Sort + Heap
643	Design Graph Shortest Path	Hard	Dijkstra
644	Ways to Arrive at Dest	Medium	Dijkstra + DP
645	Longest String Chain	Medium	DP + Map
646	Min Ops Reduce X to Zero	Medium	Sliding Window
647	Number of Enclaves	Medium	DFS / BFS
648	Find All Farmland	Medium	DFS / BFS
649	Next Permutation	Medium	Math
650	Stamping the Sequence	Hard	Greedy (Reverse)

You've Got This

650 problems is a lot. But if you do 3 problems a day, you'll finish in about 7 months. That's 7 months to be better than 99% of developers at problem-solving. Start today. One problem at a time.

Need the foundations first? Start with the DSA Foundations page.

Topics (650 Problems)