Personal Data Structures & Algorithms Study Progression

Number	Problem	Difficulty	Topic	Solution
1	Two Sum	Easy	Arrays & Hashing	#25
2	Add Two Numbers	Medium	Linked List	#90
3	Longest Substring Without Repeating Characters	Medium	Sliding Window	#74
5	Longest Palindromic Substring	Medium	1-D Dynamic Programming	#193
7	Reverse Integer	Medium	Bit Manipulation	#428
11	Container With Most Water	Medium	Two Pointers	#10
15	3Sum	Medium	Two Pointers	#55
17	Letter Combinations of a Phone Number	Medium	Backtracking	#148
19	Remove Nth Node From End of List	Medium	Linked List	#86
20	Valid Parentheses	Easy	Stack	#14
21	Merge Two Sorted Lists	Easy	Linked List	#82
22	Generate Parentheses	Medium	Backtracking	#136
33	Search in Rotated Sorted Array	Medium	Binary Search	#68
36	Valid Sudoku	Medium	Arrays & Hashing	#35
39	Combination Sum	Medium	Backtracking	#134
40	Combination Sum II	Medium	Backtracking	#142
42	Trapping Rain Water	Hard	Two Pointers	#532
45	Jump Game II	Medium	Greedy	#334
46	Permutations	Medium	Backtracking	#138
47	Permutations II	Medium	Backtracking	#635
49	Group Anagrams	Medium	Arrays & Hashing	#27
53	Maximum Subarray	Medium	Greedy	#320
55	Jump Game	Medium	Greedy	#328
56	Merge Intervals	Medium	Intervals	#283
57	Insert Interval	Medium	Intervals	#281
62	Unique Paths	Medium	2-D Dynamic Programming	#522
70	Climbing Stairs	Easy	1-D Dynamic Programming	#185
74	Search a 2D Matrix	Medium	Binary Search	#59
76	Minimum Window Substring	Hard	Sliding Window	#394
78	Subsets	Medium	Backtracking	#132
79	Word Search	Medium	Backtracking	#144
90	Subsets II	Medium	Backtracking	#140
91	Decode Ways	Medium	1-D Dynamic Programming	#199
98	Validate Binary Search Tree	Medium	Trees	#122
100	Same Tree	Easy	Trees	#110
102	Binary Tree Level Order Traversal	Medium	Trees	#116
104	Maximum Depth of Binary Tree	Easy	Trees	#99
105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	Trees	#124
110	Balanced Binary Tree	Easy	Trees	#108
111	Minimum Depth of Binary Tree	Easy	Trees	#101
121	Best Time to Buy and Sell Stock	Easy	Sliding Window	#72
125	Valid Palindrome	Easy	Two Pointers	#50
127	Word Ladder	Hard	Graphs	#457
128	Longest Consecutive Sequence	Medium	Arrays & Hashing	#38
131	Palindrome Partitioning	Medium	Backtracking	#146
133	Clone Graph	Medium	Graphs	#154
134	Gas Station	Medium	Greedy	#346
136	Single Number	Easy	Bit Manipulation	#223
138	Copy List with Random Pointer	Medium	Linked List	#88
139	Word Break	Medium	1-D Dynamic Programming	#205
141	Linked List Cycle	Medium	Linked List	#93
143	Reorder List	Medium	Linked List	#84
145	Binary Tree Postorder Traversal	Easy	Trees	#641
146	LRU Cache	Medium	Linked List	#103
150	Evaluate Reverse Polish Notation	Medium	Stack	#44
151	Reverse Words in a String	Medium	Two Pointers	#213
152	Maximum Product Subarray	Medium	1-D Dynamic Programming	#203
153	Find Minimum in Rotated Sorted Array	Medium	Binary Search	#66
155	Min Stack	Medium	Stack	#42
167	Two Sum II - Input Array Is Sorted	Medium	Two Pointers	#53
175	Combine Two Tables	Easy	Database	#3
176	Second Highest Salary	Easy	Database	#4
177	Nth Highest Salary	Medium	Database	#5
181	Employees Earning More Than Their Managers	Easy	Database	#6
182	Duplicate Emails	Easy	Database	#7
183	Customers Who Never Order	Easy	Database	#8
190	Reverse Bits	Easy	Bit Manipulation	#231
191	Number of 1 Bits	Easy	Bit Manipulation	#225
193	Valid Phone Numbers	Easy	Shell	#19
195	Tenth Line	Easy	Shell	#15
197	Rising Temperature	Easy	Database	#9
198	House Robber	Medium	1-D Dynamic Programming	#189
199	Binary Tree Right Side View	Medium	Trees	#118
200	Number of Islands	Medium	Graphs	#150
206	Reverse Linked List	Easy	Linked List	#80
207	Course Schedule	Medium	Graphs	#163
208	Implement Trie (Prefix Tree)	Medium	Tries	#128
209	Minimum Size Subarray Sum	Medium	Sliding Window	#643
210	Course Schedule II	Medium	Graphs	#165
211	Design Add and Search Words Data Structure)	Medium	Tries	#130
212	Word Search II	Hard	Tries	#255
213	House Robber II	Medium	1-D Dynamic Programming	#191
214	Shortest Palindrome	Hard	Strings	#242
215	Kth Largest Element in an Array	Medium	Heap / Priority Queue	#179
217	Contains Duplicate	Easy	Arrays & Hashing	#21
226	Invert Binary Tree	Easy	Trees	#97
230	Kth Smallest Element in a BST	Medium	Trees	#126
235	Lowest Common Ancestor of a Binary Search Tree	Medium	Trees	#114
236	Lowest Common Ancestor of a Binary Tree	Medium	Trees	#647
238	Product of Array Except Self	Medium	Prefix Sum	#32
241	Different Ways to Add Parentheses	Medium	Backtracking	#240
242	Valid Anagram	Easy	Arrays & Hashing	#23
252	Meeting Rooms	Easy	Intervals	#292
253	Meeting Rooms II	Medium	Intervals	#298
261	Graph Valid Tree	Medium	Graphs	#167
266	Palindrome Permutation	Easy	Arrays & Hashing	#605
268	Missing Number	Easy	Bit Manipulation	#368
269	Alien Dictionary	Hard	Graphs	#492
271	Encode and Decode Strings	Medium	Arrays & Hashing	#61
279	Perfect Squares	Medium	1D Dynamic Programming	#510
286	Walls and Gates	Medium	Graphs	#161
287	Find the Duplicate Number	Medium	Linked List	#95
300	Longest Increasing Subsequence	Medium	1-D Dynamic Programming	#207
309	Best Time to Buy and Sell Stock with Cooldown	Medium	2-D Dynamic Programming	#528
322	Coin Change	Medium	1-D Dynamic Programming	#201
323	Number of Connected Components in an Undirected Graph	Medium	Graphs	#169
332	Reconstruct Itinerary	Hard	Graphs	#445
344	Reverse String	Easy	Two Pointers	#645
347	Top K Frequent Elements	Medium	Arrays & Hashing	#30
355	Design Twitter	Medium	Heap / Priority Queue	#183
371	Sum of Two Integers	Medium	Bit Manipulation	#406
386	Lexicographical Numbers	Medium	Tries	#244
399	Evaluate Division	Medium	Graphs	#195
412	Fizz Buzz	Easy	Strings	#409
416	Partition Equal Subset Sum	Medium	1-D Dynamic Programming	#209
417	Pacific Atlantic Water Flow	Medium	Graphs	#158
424	Longest Repeating Character Replacement	Medium	Sliding Window	#77
432	All O`one Data Structure	Hard	Linked List	#265
435	Non-overlapping Intervals	Medium	Intervals	#290
440	K-th Smallest in Lexicographical Order	Hard	Tries	#246
494	Target Sum	Medium	2-D Dynamic Programming	#570
515	Find Largest Value in Each Tree Row	Medium	Trees	#442
518	Coin Change II	Medium	2-D Dynamic Programming	#546
539	Minimum Time Difference	Medium	Arrays & Hashing	#233
543	Diameter of Binary Tree	Easy	Trees	#105
567	Permutation in String	Medium	Sliding Window	#78
572	Subtree of Another Tree	Easy	Trees	#112
621	Task Scheduler	Medium	Heap / Priority Queue	#181
622	Design Circular Queue	Medium	Linked List	#633
632	Smallest Range Covering Elements from K Lists	Hard	Heap / Priority Queue	#306
641	Design Circular Deque	Medium	Linked List	#263
647	Palindromic Substrings	Medium	1-D Dynamic Programming	#197
670	Maximum Swap	Medium	Greedy	#314
678	Valid Parenthesis String	Medium	Greedy	#363
684	Redundant Connection	Medium	Graphs	#171
695	Max Area of Island	Medium	Graphs	#152
703	Kth Largest Element in a Stream	Easy	Heap / Priority Queue	#173
704	Binary Search	Easy	Binary Search	#57
729	My Calendar I	Medium	Trees	#257
731	My Calendar II	Medium	Intervals	#261
739	Daily Temperatures	Medium	Stack	#46
743	Network Delay Time	Medium	Graphs	#467
746	Min Cost Climbing Stairs	Easy	1-D Dynamic Programming	#187
763	Partition Labels	Medium	Greedy	#355
769	Max Chunks To Make Sorted	Medium	Arrays & Hashing	#438
778	Swim in Rising Water	Hard	Graphs	#479
784	Letter Case Permutation	Medium	Backtracking	#1
787	Cheapest Flights Within K Stops	Medium	Graphs	#500
796	Rotate String	Easy	Strings	#359
797	All Paths From Source to Target	Medium	Graphs	#2
827	Making A Large Island	Hard	Graphs	#512
846	Hand of Straights	Medium	Greedy	#350
853	Car Fleet	Medium	Stack	#48
875	Koko Eating Bananas	Medium	Binary Search	#65
884	Uncommon Words from Two Sentences	Easy	Strings	#238
889	Construct Binary Tree from Preorder and Postorder Traversal	Medium	Trees	#569
916	Word Subsets	Medium	Strings	#469
921	Minimum Add to Make Parentheses Valid	Medium	Stack	#294
951	Flip Equivalent Binary Trees	Medium	Trees	#336
962	Maximum Width Ramp	Medium	Stack	#296
973	K Closest Points to Origin	Medium	Heap / Priority Queue	#177
981	Time Based Key-Value Store	Medium	Binary Search	#70
994	Rotting Oranges	Medium	Graphs	#156
997	Find the Town Judge	Easy	Graphs	#629
1014	Best Sightseeing Pair	Medium	1D Dynamic Programming	#443
1028	Recover a Tree From Preorder Traversal	Hard	Trees	#567
1046	Last Stone Weight	Easy	Heap / Priority Queue	#175
1072	Flip Columns For Maximum Number of Equal Rows	Medium	Arrays & Hashing	#392
1079	Letter Tile Possibilities	Medium	Backtracking	#557
1100	Find K-Length Substrings With No Repeated Characters	Medium	Sliding Window	#591
1123	Lowest Common Ancestor of Deepest Leaves	Medium	Trees	#648
1133	Largest Unique Number	Easy	Arrays & Hashing	#273
1137	N-th Tribonacci Number	Easy	Dynamic Programming	#502
1143	Longest Common Subsequence	Medium	2-D Dynamic Programming	#526
1213	Intersection of Three Sorted Arrays	Easy	Arrays & Hashing	#380
1233	Remove Sub-Folders from the Filesystem	Medium	Arrays & Hashing	#338
1261	Find Elements in a Contaminated Binary Tree	Medium	Trees	#562
1267	Count Servers that Communicate	Medium	Arrays & Hashing	#498
1277	Count Square Submatrices with All Ones	Medium	1D Dynamic Programming	#342
1310	XOR Queries of a Subarray	Medium	Bit Manipulation	#227
1331	Rank Transform of an Array	Easy	Arrays & Hashing	#275
1346	Check If N and Its Double Exist	Easy	Arrays & Hashing	#402
1352	Product of the Last K Numbers	Medium	Prefix Sum	#550
1358	Number of Substrings Containing All Three Characters	Medium	Sliding Window	#596
1368	Minimum Cost to Make at Least One Valid Path in a Grid	Hard	Graphs	#485
1371	Find the Longest Substring Containing Vowels in Even Counts	Medium	Bit Manipulation	#235
1381	Design a Stack With Increment Operation	Medium	Stack	#267
1405	Longest Happy String	Medium	Heap / Priority Queue	#312
1406	Stone Game III	Hard	1D Dynamic Programming	#517
1408	String Matching in an Array	Easy	Strings	#459
1415	The k-th Lexicographical String of All Happy Strings of Length n	Medium	Backtracking	#559
1422	Maximum Score After Splitting a String	Easy	Prefix Sum	#447
1427	Perform String Shifts	Easy	Strings	#454
1429	First Unique Number	Medium	Arrays & Hashing	#326
1448	Count Good Nodes in Binary Tree	Medium	Trees	#120
1455	Check If a Word Occurs As a Prefix of Any Word in a Sentence	Easy	Strings	#404
1462	Course Schedule IV	Medium	Graphs	#506
1475	Final Prices With a Special Discount in a Shop	Easy	Stack	#436
1497	Check If Array Pairs Are Divisible by k	Medium	Arrays & Hashing	#271
1524	Number of Sub-arrays With Odd Sum	Medium	Prefix Sum	#576
1545	Find Kth Bit in Nth Binary String	Medium	Strings	#322
1584	Min Cost to Connect All Points	Medium	Graphs	#473
1590	Make Sum Divisible by P	Medium	Prefix Sum	#277
1593	Split a String Into the Max Number of Unique Substrings	Medium	Backtracking	#324
1652	Defuse the Bomb	Easy	Sliding Window	#384
1684	Count the Number of Consistent Strings	Easy	Arrays & Hashing	#221
1718	Construct the Lexicographically Largest Valid Sequence	Medium	Backtracking	#555
1726	Tuple with Same Product	Medium	Arrays & Hashing	#534
1730	Shortest Path to Get Food	Medium	Graphs	#487
1749	Maximum Absolute Sum of Any Subarray	Medium	1-D Dynamic Programming	#574
1752	Check if Array Is Sorted and Rotated	Easy	Arrays & Hashing	#516
1760	Minimum Limit of Balls in a Bag	Medium	Binary Search	#415
1765	Map of Highest Peak	Medium	Graphs	#496
1769	Minimum Number of Operations to Move All Balls to Each Box	Medium	Prefix Sum	#463
1790	Check if One String Swap Can Make Strings Equal	Easy	Arrays & Hashing	#530
1800	Maximum Ascending Subarray Sum	Easy	Sliding Window	#524
1804	Implement Trie II (Prefix Tree)	Medium	Tries	#269
1813	Sentence Similarity III	Medium	Two Pointers	#285
1829	Maximum XOR for Each Query	Medium	Bit Manipulation	#371
1851	Minimum Interval to Include Each Query	Hard	Intervals	#318
1852	Distinct Numbers in Each Subarray	Medium	Sliding Window	#518
1858	Longest Word With All Prefixes	Medium	Tries	#259
1861	Rotating the Box	Medium	Arrays & Hashing	#398
1863	Sum of All Subset XOR Totals	Easy	Backtracking	#650
1899	Merge Triplets to Form Target Triplet	Medium	Greedy	#353
1910	Remove All Occurrences of a Substring	Medium	Stack	#543
1930	Unique Length-3 Palindromic Subsequences	Medium	Arrays & Hashing	#455
1942	The Number of the Smallest Unoccupied Chair	Medium	Heap / Priority Queue	#302
1957	Delete Characters to Make Fancy String	Easy	String	#351
1963	Minimum Number of Swaps to Make the String Balanced	Medium	Stack	#288
1975	Maximum Matrix Sum	Medium	Arrays & Hashing	#396
1976	Number of Ways to Arrive at Destination	Medium	Graphs	#617
1980	Find Unique Binary String	Medium	Backtracking	#564
2017	Grid Game	Medium	Prefix Sum	#494
2033	Minimum Operations to Make a Uni-Value Grid	Medium	Math & Geometry	#623
2044	Count Number of Maximum Bitwise-OR Subsets	Medium	Backtracking	#316
2109	Adding Spaces to a String	Medium	Strings	#408
2115	Find All Possible Recipes from Given Supplies	Medium	Graphs	#613
2161	Partition Array According to Given Pivot	Medium	Stack	#582
2185	Counting Words With a Given Prefix	Easy	Strings	#465
2206	Divide Array Into Equal Pairs	Easy	Arrays & Hashing	#603
2220	Minimum Bit Flips to Convert Number	Easy	Bit Manipulation	#219
2226	Maximum Candies Allocated to K Children	Medium	Binary Search	#600
2257	Count Unguarded Cells in the Grid	Medium	Arrays & Hashing	#390
2270	Number of Ways to Split Array	Medium	Prefix Sum	#451
2275	Largest Combination With Bitwise AND Greater Than Zero	Medium	Bit Manipulation	#369
2326	Spiral Matrix IV	Medium	Linked List	#215
2337	Move Pieces to Obtain a String	Medium	Two Pointers	#411
2342	Max Sum of a Pair With Equal Sum of Digits	Medium	Heap / Priority Queue	#545
2349	Design a Number Container System	Medium	Heap / Priority Queue	#538
2364	Count Number of Bad Pairs	Medium	Math & Geometry	#540
2375	Construct Smallest Number From DI String	Medium	Backtracking	#554
2379	Minimum Recolors to Get K Consecutive Black Blocks	Easy	Sliding Window	#589
2401	Longest Nice Subarray	Medium	Bit Manipulation	#607
2406	Divide Intervals Into Minimum Number of Groups	Medium	Heap / Priority Queue	#304
2415	Reverse Odd Levels of Binary Tree	Medium	Trees	#440
2416	Sum of Prefix Scores of Strings	Hard	Tries	#253
2419	Longest Subarray With Maximum Bitwise AND	Medium	Bit Manipulation	#229
2425	Bitwise XOR of All Pairings	Medium	Bit Manipulation	#481
2429	Minimize XOR	Medium	Bit Manipulation	#477
2460	Apply Operations to an Array	Easy	Two Pointers	#578
2461	Maximum Sum of Distinct Subarrays With Length K	Medium	Sliding Window	#386
2467	Most Profitable Path in a Tree	Medium	Trees	#572
2490	Circular Sentence	Easy	Strings	#357
2491	Divide Players Into Teams of Equal Skill	Medium	Arrays & Hashing	#279
2501	Longest Square Streak in an Array	Medium	1D Dynamic Programming	#344
2503	Maximum Number of Points From Grid Queries	Hard	Graphs	#627
2516	Take K of Each Character From Left and Right	Medium	Sliding Window	#388
2523	Closest Prime Numbers in Range	Medium	Math & Geometry	#588
2529	Maximum Count of Positive Integer and Negative Integer	Easy	Binary Search	#598
2530	Maximal Score After Applying K Operations	Medium	Heap / Priority Queue	#308
2554	Maximum Number of Integers to Choose From a Range I	Medium	Arrays & Hashing	#413
2558	Take Gifts From the Richest Pile	Easy	Heap / Priority Queue	#421
2559	Count Vowel Strings in Ranges	Medium	Prefix Sum	#449
2563	Count the Number of Fair Pairs	Medium	Binary Search	#378
2570	Merge Two 2D Arrays by Summing Values	Easy	Two Pointers	#580
2579	Count Total Number of Colored Cells	Medium	Math & Geometry	#584
2583	Kth Largest Sum in a Binary Tree	Medium	Trees	#330
2593	Find Score of an Array After Marking All Elements	Medium	Heap / Priority Queue	#424
2601	Prime Subtraction Operation	Medium	Greedy	#376
2641	Cousins in Binary Tree II	Medium	Trees	#332
2657	Find the Prefix Common Array of Two Arrays	Medium	Arrays & Hashing	#471
2658	Maximum Number of Fish in a Grid	Medium	Graphs	#508
2661	First Completely Painted Row or Column	Medium	Arrays & Hashing	#490
2664	The Knight’s Tour	Medium	Backtracking	#340
2683	Neighboring Bitwise XOR	Medium	Bit Manipulation	#483
2684	Maximum Number of Moves in a Grid	Medium	1D Dynamic Programming	#348
2685	Count the Number of Complete Components	Medium	Graphs	#615
2696	Minimum String Length After Removing Substrings	Easy	Stack	#286
2698	Find the Punishment Number of an Integer	Medium	Backtracking	#552
2707	Extra Characters in a String	Medium	1D Dynamic Programming	#249
2737	Find the Closest Marked Node	Medium	Graphs	#631
2762	Continuous Subarrays	Medium	Heap / Priority Queue	#430
2779	Maximum Beauty of an Array After Applying Operation	Medium	Sliding Window	#420
2780	Minimum Index of a Valid Split	Medium	Arrays & Hashing	#625
2807	Insert Greatest Common Divisors in Linked List	Medium	Linked List	#217
2838	Maximum Coins Heroes Can Collect	Medium	Binary Search	#300
2873	Maximum Value of an Ordered Triplet I	Easy	Greedy	#637
2874	Maximum Value of an Ordered Triplet II	Medium	Greedy	#639
2914	Minimum Number of Changes to Make Binary String Beautiful	Medium	Strings	#365
2924	Find Champion II	Medium	Graph	#399
2938	Separate Black and White Balls	Medium	Two Pointers	#310
2948	Make Lexicographically Smallest Array by Swapping Elements	Medium	Arrays & Hashing	#504
2965	Find Missing and Repeated Values	Easy	Arrays & Hashing	#586
2981	Find Longest Special Substring That Occurs Thrice I	Medium	Sliding Window	#426
3011	Find if Array Can Be Sorted	Medium	Bit Manipulation	#367
3042	Count Prefix and Suffix Pairs I	Easy	Strings	#461
3043	Find the Length of the Longest Common Prefix	Medium	Tries	#251
3066	Minimum Operations to Exceed Threshold Value II	Medium	Heap / Priority Queue	#548
3097	Shortest Subarray With OR at Least K II	Medium	Bit Manipulation	#374
3105	Longest Strictly Increasing or Strictly Decreasing Subarray	Easy	Sliding Window	#520
3108	Minimum Cost Walk in Weighted Graph	Hard	Graphs	#611
3151	Special Array I	Easy	Sliding Window	#514
3152	Special Array II	Medium	Prefix Sum	#417
3160	Find the Number of Distinct Colors Among the Balls	Medium	Arrays & Hashing	#536
3163	String Compression III	Medium	Strings	#361
3169	Count Days Without Meetings	Medium	Intervals	#619
3174	Clear Digits	Easy	Stack	#541
3191	Minimum Operations to Make Binary Array Elements Equal to One I	Medium	Sliding Window	#609
3208	Alternating Groups II	Medium	Sliding Window	#594
3217	Delete Nodes From Linked List Present in Array	Medium	Linked List	#211
3223	Minimum Length of String After Operations	Medium	Arrays & Hashing	#475
3254	Find the Power of K-Size Subarrays I	Medium	Sliding Window	#382
3264	Final Array State After K Multiplication Operations I	Easy	Heap / Priority Queue	#432
3394	Check if Grid can be Cut into Sections	Medium	Intervals	#621