15.1 Quick Lookup by Problem ID

Browse problems by platform, sorted by problem ID (numeric when present, otherwise by title):

15.1.1 LeetCode

ID	Problem	Difficulty	Chapter
1	Two Sums I	Easy	Array
2	Add Two Numbers	Medium	Linked List
3	Longest Substring Without Repeating	Medium	String Manipulation
4	Median of Two Sorted Arrays	Hard	Array
5	Longest Palindromic Substring	Medium	Dynamic Programming and Backtracking
7	Reverse Integer	Medium	Math
8	String to Integer (atoi)	Medium	String Manipulation
11	Container With Most Water	Medium	Array
14	Longest Common Prefix	Easy	String Manipulation
15	3Sum	Medium	Array
16	3Sum Closest	Medium	Array
17	Letter Combinations of a Phone Number	Medium	Dynamic Programming and Backtracking
18	4Sum	Medium	Array
19	Remove Nth Node From End	Medium	Linked List
21	Merge Two Sorted Lists	Easy	Linked List
23	Merge k Sorted Lists	Hard	Linked List
25	Reverse Nodes in k-Group	Hard	Linked List
26	Remove Duplicates from Sorted Array	Easy	Array
32	Longest Valid Parentheses	Hard	Stack and Queue
33	Search in Rotated Sorted Array	Medium	Array
36	Valid Sudoku	Medium	Matrix
39	Combination Sum	Medium	Dynamic Programming and Backtracking
46	Permutations	Medium	Dynamic Programming and Backtracking
47	Permutations II	Medium	Dynamic Programming and Backtracking
48	Rotate Image	Medium	Matrix
49	Group Anagrams	Medium	String Manipulation
50	Pow(x; n)	Medium	Math
53	Maximum Subarray	Easy	Array
54	Spiral Matrix	Medium	Matrix
56	Merge Intervals	Medium	Array
57	Insert Interval	Hard	Array
62	Unique Paths	Medium	Dynamic Programming and Backtracking
64	Minimum Path Sum	Medium	Dynamic Programming and Backtracking
66	Plus One	Easy	Array
70	Climbing Stairs	Easy	Dynamic Programming and Backtracking
73	Set Matrix Zeroes	Medium	Matrix
74	Search a 2D Matrix	Medium	Matrix
75	Sort Colors	Medium	Array
78	Subsets	Medium	Dynamic Programming and Backtracking
79	Word Search	Medium	Dynamic Programming and Backtracking
83	Remove Duplicates from Sorted List	Easy	Linked List
90	Subsets II	Medium	Dynamic Programming and Backtracking
91	Decode Ways	Medium	Dynamic Programming and Backtracking
92	Reverse Linked List II	Medium	Linked List
94	Binary Tree Inorder Traversal	Easy	Tree
98	Validate Binary Search Tree	Medium	Tree
102	Binary Tree Level Order Traversal	Medium	Tree
107	Binary Tree Level Order Traversal II	Medium	Tree
110	Balanced Binary Tree	Easy	Tree
111	Minimum Depth of Binary Tree	Easy	Tree
112	Path Sum	Easy	Tree
116	Populating Next Right Pointers in Each Node	Medium	Tree
118	Pascal’s Triangle	Easy	Dynamic Programming and Backtracking
121	Best Time to Buy and Sell Stock	Easy	Array
122	Best Time to Buy and Sell Stock II	Easy	Array
127	Word Ladder	Medium	String Manipulation
130	Surrounded Regions	Medium	Matrix
133	Clone Graph	Medium	Graph
134	Gas Station	Medium	Array
136	Single Number	Easy	Math
138	Copy List with Random Pointer	Medium	Linked List
139	Word Break	Medium	Dynamic Programming and Backtracking
141	Linked List Cycle	Easy	Linked List
142	Linked List Cycle II	Medium	Linked List
143	Reorder List	Medium	Linked List
144	Binary Tree Preorder Traversal	Easy	Tree
145	Binary Tree Postorder Traversal	Easy	Tree
146	Design LRU Cache	Medium	Advanced Data Structure
147	Insertion Sort List	Medium	Linked List
148	Sort List	Medium	Linked List
150	Evaluate Reverse Polish Notation	Medium	Stack and Queue
152	Maximum Product Subarray	Medium	Array
155	Min Stack	Medium	Stack and Queue
156	Binary Tree Upside Down	Medium	Tree
160	Intersection of Two Linked Lists	Easy	Linked List
167	Two Sum II - Sorted Array	Medium	Array
190	Reverse Bits	Easy	Math
191	Number of 1 Bits	Easy	Math
198	House Robber	Easy	Dynamic Programming and Backtracking
200	Number of Islands	Medium	Matrix
202	Happy Number	Easy	Math
204	Count Primes	Easy	Math
206	Reverse Linked List	Easy	Linked List
207	Course Schedule	Medium	Graph
208	Implement Trie (Prefix Tree)	Medium	Tree
209	Minimum Size Subarray Sum	Medium	Array
210	Course Schedule II	Medium	Graph
211	Design Add and Search Words Data Structure	Medium	String Manipulation
215	Find kth Largest Element	Medium	Heap
221	Maximal Square	Medium	Dynamic Programming and Backtracking
230	Kth Smallest Element in a BST	Medium	Tree
232	Implement Queue using Stacks	Easy	Stack and Queue
234	Palindrome Linked List	Easy	Linked List
235	Lowest Common Ancestor of a Binary Search Tree	Medium	Tree
236	Lowest Common Ancestor of a Binary Tree	Medium	Tree
238	Product of Array Except Self	Medium	Array
240	Search a 2D Matrix II	Medium	Matrix
250	Count Univalue Subtrees	Medium	Tree
253	Meeting Rooms II	Medium	Heap
256	Paint House	Easy	Dynamic Programming and Backtracking
261	Graph Valid Tree	Medium	Graph
269	Alien Dictionary	Hard	Graph
271	Encode and Decode Strings	Medium	String Manipulation
278	First Bad Version	Easy	Interactive
285	Inorder Successor in BST	Medium	Tree
286	Walls and Gates	Medium	Matrix
287	Find the Duplicate Number	Medium	Array
295	Find Median from Data Stream	Hard	Heap
296	Best Meeting Point	Hard	Matrix
297	Serialize and Deserialize Binary Tree	Hard	Tree
298	Binary Tree Longest Consecutive Sequence	Medium	Tree
300	Longest Increasing Subsequence	Medium	Dynamic Programming and Backtracking
309	Best Time to Buy and Sell Stock with Cooldown	Medium	Dynamic Programming and Backtracking
322	Coin Change	Medium	Dynamic Programming and Backtracking
323	Number of Connected Components in an Undirected Graph	Medium	Graph
328	Odd Even Linked List	Medium	Linked List
347	Top K Frequent Elements	Medium	Heap
348	Design Tic-Tac-Toe	Medium	Matrix
355	Design Twitter	Medium	Advanced Data Structure
366	Find Leaves of Binary Tree	Medium	Tree
371	Sum of Two Integers	Medium	Math
383	Ransom Note	Easy	String Manipulation
398	Random Pick Index	Medium	Array
409	Longest Palindrome	Easy	String Manipulation
417	Pacific Atlantic Water Flow	Medium	Matrix
419	Battleships in a Board	Medium	Matrix
424	Longest Repeating Character Replacement	Medium	String Manipulation
435	Non-overlapping Intervals	Medium	Array
438	Find All Anagrams in a String	Medium	String Manipulation
451	Sort Characters By Frequency	Medium	String Manipulation
454	4Sum II	Medium	Array
470	Implement Rand10() Using Rand7()	Medium	Math
518	Coin Change II	Medium	Dynamic Programming and Backtracking
528	Random Pick with Weight	Medium	Array
542	01 Matrix	Medium	Matrix
543	Diameter of Binary Tree	Easy	Tree
554	Brick Wall	Medium	Matrix
567	Permutation in String	Medium	String Manipulation
572	Subtree of Another Tree	Easy	Tree
621	Task Scheduler	Medium	Stack and Queue
647	Palindromic Substrings	Medium	Dynamic Programming and Backtracking
653	Two Sum IV - BST	Easy	Tree
680	Valid Palindrome II	Easy	String Manipulation
704	Binary Search	Easy	Array
705	Design HashSet	Easy	Advanced Data Structure
706	Design HashMap	Easy	Advanced Data Structure
721	Accounts Merge	Medium	Graph
729	My Calendar I	Medium	Advanced Data Structure
739	Daily Temperatures	Medium	Stack and Queue
743	Network Delay Time	Medium	Graph
801	Minimum Swaps Sequences Increasing	Medium	Dynamic Programming and Backtracking
843	Guess the Word	Hard	Interactive
846	Hand of Straights	Medium	Array
849	Maximize Distance to Closest Person	Medium	Array
853	Car Fleet	Medium	Stack and Queue
875	Koko Eating Bananas	Medium	Array
905	Sort Array By Parity	Easy	Array
953	Verifying an Alien Dictionary	Easy	String Manipulation
973	K Closest Points to Origin	Medium	Heap
981	Time Based Key-Value Store	Medium	Advanced Data Structure
986	Interval List Intersections	Medium	Array
994	Rotting Oranges	Medium	Matrix
1002	Find Common Characters	Easy	Array
1046	Last Stone Weight	Easy	Heap
1277	Count Square Submatrices with All Ones	Medium	Dynamic Programming and Backtracking
1347	Minimum Number of Steps to Make Two Strings Anagram	Medium	String Manipulation
1358	Number of Substrings All Three Chars	Medium	String Manipulation
1448	Count Good Nodes in Binary Tree	Medium	Tree
1669	Merge In Between Linked Lists	Medium	Linked List
1717	Maximum Score From Removing Substrings	Medium	Stack and Queue
1891	Cutting Ribbons	Medium	Array
1899	Merge Triplets to Form Target Triplet	Medium	Array
1921	Eliminate Maximum Monsters	Medium	Array
2013	Detect Squares	Medium	Matrix
2043	Simple Bank System	Medium	Advanced Data Structure
2348	Number of Zero-Filled Subarrays	Medium	Array
2966	Divide Array Into Arrays With Max Difference	Medium	Array
3191	Minimum Operations to Make Binary Array Elements Equal to One I	Medium	Array
-	Shortest Word Distance	Easy	Array

15.1.2 HackerRank

ID	Problem	Difficulty	Chapter
-	Check Palindrome by Filtering Non-Letters	Easy	String Manipulation
-	Count Elements Greater Than Previous Average	Easy	Array
-	Count Number Pairs	Easy	Array
-	Custom Fibonacci Sequence	Easy	Dynamic Programming and Backtracking
-	Find Index Combinations with Target Weight Sum	Medium	Dynamic Programming and Backtracking
-	Generate Valid Angle Bracket Sequences	Easy	Dynamic Programming and Backtracking
-	Height of Binary Search Tree	Easy	Tree
-	Max Unique Substring Length in a Session	Medium	String Manipulation
-	Merge and Sort Intervals	Medium	Array
-	Minimum Plans to Reach Target Bandwidth	Medium	Dynamic Programming and Backtracking
-	Next Greater Element with Position Offset	Medium	Stack and Queue
-	One-Pass Removal of k-th Node from End	Medium	Linked List
-	Reverse Even-Indexed Nodes and Append	Medium	Linked List
-	Top K Frequent Events with Order Preservation	Medium	Heap
-	Validate Properly Nested Brackets	Easy	Stack and Queue

15.1.3 Firecode

ID	Problem	Difficulty	Chapter
-	Binary Representation	Easy	String Manipulation
-	Fibonacci Sequence	Easy	Dynamic Programming and Backtracking
-	Insert Stars	Easy	String Manipulation
-	Max Gain	Easy	Array
-	Maximum Number of Repetitions	Medium	Array
-	Power of Two	Easy	Math
-	Retrieve Optimal Computation	Medium	Dynamic Programming and Backtracking
-	Selection Sort Array	Easy	Array

15.1.4 Other

ID	Problem	Difficulty	Chapter
-	Distance of Nearest Cell Having 1	Medium	Graph
-	Graph Serialization	Unclassified	Graph
-	Insert Node at Position in Doubly Linked List	Easy	Linked List
-	Retrieve Elements K Times	Easy	Array
-	Two Sum II - Boolean	Easy	Array
-	Two Sum V	Medium	Array

15.1.5 Interview

ID	Problem	Difficulty	Chapter
-	First Non-Repeated Character	Easy	String Manipulation
-	Hardware Build Feasibility	Medium	Graph
-	Implement Queue	Easy	Advanced Data Structure
-	Implement Stack Using Queues	Easy	Advanced Data Structure
-	Lock-Free Stack Using Linked List (CAS)	Easy	Stack and Queue
-	Longest Common Substring	Medium	Dynamic Programming and Backtracking
-	Merge K Sorted Arrays	Medium	Heap
-	Minimum Operations to One	Medium	Dynamic Programming and Backtracking
-	Quick Sort Array	Medium	Array
-	Top K Elements	Medium	Heap
-	VIP Customer Scheduler	Medium	Heap

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