Top 50 LeetCode Problems Organized by Pattern

Feb 19, 202612 min read

LeetCode has thousands of problems, but a core set of 50 covers the patterns you will see in most coding interviews. This list groups them by the 7 pattern categories used in AlgoArk, so you can study by pattern instead of by random problem number.

How to Use This List

Pick one category, learn the pattern (use our pattern pages), then solve 3–5 problems from that category before moving on. Do not jump between categories. Master one pattern at a time.

Array & String

Problem	#	Difficulty	Pattern
Two Sum	1	Easy	Two Pointers / Hash Map
3Sum	15	Medium	Two Pointers
Container With Most Water	11	Medium	Two Pointers
Valid Palindrome	125	Easy	Two Pointers
Longest Substring Without Repeating Characters	3	Medium	Sliding Window
Minimum Window Substring	76	Hard	Sliding Window
Subarray Sum Equals K	560	Medium	Prefix Sum
Maximum Subarray	53	Medium	Kadane's
Product of Array Except Self	238	Medium	Prefix Sum

Hashing & Frequency

Problem	#	Difficulty	Pattern
Group Anagrams	49	Medium	Hash Map
Top K Frequent Elements	347	Medium	Top K / Hash Map
Valid Anagram	242	Easy	Hash Map
Contains Duplicate	217	Easy	Hash Map
Two Sum	1	Easy	Two Sum Pattern
3Sum	15	Medium	Two Sum Variant

Sorting & Searching

Problem	#	Difficulty	Pattern
Binary Search	704	Easy	Binary Search
Search Insert Position	35	Easy	Binary Search
Find Minimum in Rotated Sorted Array	153	Medium	Binary Search
Merge Intervals	56	Medium	Merge Intervals
Insert Interval	57	Medium	Merge Intervals
K Closest Points to Origin	973	Medium	Top K
Find Kth Largest Element	215	Medium	Top K / QuickSelect

Tree & Graph

Problem	#	Difficulty	Pattern
Binary Tree Level Order Traversal	102	Medium	BFS
Number of Islands	200	Medium	BFS / DFS
Maximum Depth of Binary Tree	104	Easy	DFS
Validate Binary Search Tree	98	Medium	DFS
Lowest Common Ancestor of BST	235	Easy	DFS
Combination Sum	39	Medium	Backtracking
Course Schedule	207	Medium	Topological Sort
Clone Graph	133	Medium	BFS / DFS

Dynamic Programming

Problem	#	Difficulty	Pattern
Climbing Stairs	70	Easy	Fibonacci
House Robber	198	Medium	Fibonacci
Coin Change	322	Medium	Unbounded Knapsack
Partition Equal Subset Sum	416	Medium	0/1 Knapsack
Longest Common Subsequence	1143	Medium	LCS
Edit Distance	72	Hard	LCS
Binary Tree Maximum Path Sum	124	Hard	DP on Trees
Unique Paths	62	Medium	Grid DP
Minimum Path Sum	64	Medium	Grid DP

Linked List

Problem	#	Difficulty	Pattern
Reverse Linked List	206	Easy	Reversal
Merge Two Sorted Lists	21	Easy	Merge
Linked List Cycle	141	Easy	Fast-Slow Pointers
Reorder List	143	Medium	Fast-Slow + Reversal

Advanced

Problem	#	Difficulty	Pattern
Implement Trie	208	Medium	Trie
Design Add and Search Words	211	Medium	Trie
LRU Cache	146	Medium	Hash Map + Linked List
Merge K Sorted Lists	23	Hard	K-Way Merge
Find Median from Data Stream	295	Hard	Two Heaps
Number of Connected Components	323	Medium	Union Find

Recommended Study Order

Array & String — Two Pointers, Sliding Window, Prefix Sum. These appear constantly.
Hashing & Frequency — Hash maps and Two Sum variants. Quick wins.
Tree & Graph — BFS, DFS, Backtracking. Core traversal patterns.
Sorting & Searching — Binary Search, Merge Intervals, Top K.
Dynamic Programming — Start with Fibonacci, then Knapsack, then LCS.
Linked List — Reversal, Fast-Slow Pointers.
Advanced — Trie, Union Find, Two Heaps. Save for later.

Not sure which pattern fits?

Use our decision tree to identify the pattern for any problem.

Try the Decision Tree