20 Essential Problems

LeetCodeSprints

Master the 20 most important Easy problems. Visual explanations, curated videos, and a clear path from zero to interview-ready.

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Patterns You'll Learn

9 fundamental patterns across 20 problems

📊
Arrays & Hashing
0/6 solved
6
📚
Stack
0/1 solved
1
🔗
Linked List
0/4 solved
4
🌳
Trees
0/4 solved
4
🔍
Binary Search
0/1 solved
1
👁
Sliding Window
0/1 solved
1
🧠
Dynamic Programming
0/1 solved
1
⚙
Bit Manipulation
0/1 solved
1
🔢
Math & Geometry
0/1 solved
1

All 20 Problems

Ordered from beginner-friendly to interview-ready

1
Two Sum#1
Hash Map Lookup
▶ 4Easy
2
Palindrome Number#9
Number Reversal
▶ 2Easy
3
Roman to Integer#13
Lookup Table
▶ 2Easy
4
Valid Parentheses#20
Stack Matching
▶ 2Easy
5
Merge Two Sorted Lists#21
Two-Pointer Merge
▶ 2Easy
6
Climbing Stairs#70
Fibonacci DP
▶ 3Easy
7
Same Tree#100
Recursive Comparison
▶ 1Easy
8
Maximum Depth of Binary Tree#104
Recursive Depth
▶ 2Easy
9
Best Time to Buy and Sell Stock#121
Track Minimum
▶ 4Easy
10
Single Number#136
XOR
▶ 3Easy
11
Linked List Cycle#141
Fast & Slow Pointers
▶ 2Easy
12
Majority Element#169
Boyer-Moore Voting
▶ 1Easy
13
Reverse Linked List#206
Pointer Reversal
▶ 1Easy
14
Contains Duplicate#217
Hash Set
▶ 1Easy
15
Invert Binary Tree#226
Recursive Swap
▶ 1Easy
16
Valid Anagram#242
Frequency Count
▶ 1Easy
17
Ransom Note#383
Frequency Count
▶ 1Easy
18
Diameter of Binary Tree#543
Global State DFS
▶ 1Easy
19
Binary Search#704
Classic Binary Search
▶ 1Easy
20
Middle of the Linked List#876
Fast & Slow Pointers
▶ 1Easy