Personal Data Structures & Algorithms Study Progression

Number	Problem	Difficulty	Topic	Solution
1	Two Sum	Easy	Arrays	#25
2	Add Two Numbers	Medium	Linked List	#90
3	Longest Substring Without Repeating Characters	Medium	Sliding Window	#74
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	#35
39	Combination Sum	Medium	Backtracking	#134
40	Combination Sum II	Medium	Backtracking	#142
46	Permutations	Medium	Backtracking	#138
49	Group Anagrams	Medium	Arrays	#27
74	Search a 2D Matrix	Medium	Binary Search	#59
78	Subsets	Medium	Backtracking	#132
79	Word Search	Medium	Backtracking	#144
90	Subsets II	Medium	Backtracking	#140
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
128	Longest Consecutive Sequence	Medium	Arrays	#38
131	Palindrome Partitioning	Medium	Backtracking	#146
133	Clone Graph	Medium	Graphs	#154
138	Copy List with Random Pointer	Medium	Linked List	#88
141	Linked List Cycle	Medium	Linked List	#93
143	Reorder List	Medium	Linked List	#84
146	LRU Cache	Medium	Linked List	#103
150	Evaluate Reverse Polish Notation	Medium	Stack	#44
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
193	Valid Phone Numbers	Easy	Shell	#19
195	Tenth Line	Easy	Shell	#15
197	Rising Temperature	Easy	Database	#9
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
210	Course Schedule II	Medium	Graphs	#165
211	Design Add and Search Words Data Structure)	Medium	Tries	#130
215	Kth Largest Element in an Array	Medium	Heap / Priority Queue	#179
217	Contains Duplicate	Easy	Arrays	#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
238	Product of Array Except Self	Medium	Arrays	#32
242	Valid Anagram	Easy	Arrays	#23
261	Graph Valid Tree	Medium	Graphs	#167
271	Encode and Decode Strings	Medium	Arrays	#61
286	Walls and Gates	Medium	Graphs	#161
287	Find the Duplicate Number	Medium	Linked List	#95
323	Number of Connected Components in an Undirected Graph	Medium	Graphs	#169
347	Top K Frequent Elements	Medium	Arrays	#30
417	Pacific Atlantic Water Flow	Medium	Graphs	#158
424	Longest Repeating Character Replacement	Medium	Sliding Window	#77
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
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
739	Daily Temperatures	Medium	Stack	#46
784	Letter Case Permutation	Medium	Backtracking	#1
797	All Paths From Source to Target	Medium	Graphs	#2
853	All Paths From Source to Target	Medium	Stack	#48
875	Koko Eating Bananas	Medium	Binary Search	#65
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
1046	Last Stone Weight	Easy	Heap / Priority Queue	#175
1448	Count Good Nodes in Binary Tree	Medium	Trees	#120