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HomePatternsQuestionsCheatsheetNotes
patternlens©
01Home02Patterns03Questions04Cheatsheet05Notes06Roadmaps07Dashboard

© 2026 PatternLens

patternlens©
Explore
HomePatternsQuestionsCheatsheetNotes

01 — the question bank

curated questions.
interview ready.

300 handpicked LeetCode problems grouped by pattern. Avoid grinding aimlessly — scan, filter, and study the specific templates you need to crack coding interviews.

Easy48
Medium196
Hard56
Patterns59
QuestionsEasyMediumHardPatterns
Showing 100 of 300 Problems

pattern 01

Arrays

10 problems
4 easy5 medium1 hard
0 / 10 Solved
0%
01

Best Time to Buy and Sell Stock

EASY
02

Majority Element

EASY
03

Move Zeroes

EASY
04

Remove Duplicates from Sorted Array

EASY
05

Best Time to Buy and Sell Stock II

MEDIUM
06

Increasing Triplet Subsequence

MEDIUM
07

Number of Zero-Filled Subarrays

MEDIUM
08

Product of Array Except Self

MEDIUM
09

Rotate Array

MEDIUM
10

First Missing Positive

HARD

pattern 02

Strings

6 problems
3 easy2 medium1 hard
0 / 6 Solved
0%
01

Is Subsequence

EASY
02

Longest Common Prefix

EASY
03

Valid Palindrome

EASY
04

Reverse Words in a String

MEDIUM
05

Zigzag Conversion

MEDIUM
06

Guess the Word

HARD

pattern 03

Linked List

10 problems
1 easy9 medium
0 / 10 Solved
0%
01

Intersection of Two Linked Lists

EASY
02

Add Two Numbers

MEDIUM
03

Copy List with Random Pointer

MEDIUM
04

Design Linked List

MEDIUM
05

Flatten a Multilevel Doubly Linked List

MEDIUM
06

Partition List

MEDIUM
07

Remove Duplicates from Sorted List II

MEDIUM
08

Remove Nth Node From End of List

MEDIUM
09

Rotate List

MEDIUM
10

Swap Nodes in Pairs

MEDIUM

pattern 04

Stacks

8 problems
2 easy5 medium1 hard
0 / 8 Solved
0%
01

Remove All Adjacent Duplicates In String

EASY
02

Valid Parentheses

EASY
03

Basic Calculator II

MEDIUM
04

Evaluate Reverse Polish Notation

MEDIUM
05

Min Stack

MEDIUM
06

Remove Duplicate Letters

MEDIUM
07

Removing Stars From a String

MEDIUM
08

Longest Valid Parentheses

HARD

pattern 05

Queues

3 problems
2 easy1 medium
0 / 3 Solved
0%
01

Number of Recent Calls

EASY
02

Time Needed to Buy Tickets

EASY
03

Reveal Cards In Increasing Order

MEDIUM

pattern 06

Hash Tables

13 problems
6 easy7 medium
0 / 13 Solved
0%
01

Contains Duplicate II

EASY
02

Design HashMap

EASY
03

Isomorphic Strings

EASY
04

Maximum Number of Balloons

EASY
05

Number of Good Pairs

EASY
06

Ransom Note

EASY
07

Encode and Decode TinyURL

MEDIUM
08

Group Anagrams

MEDIUM
09

Longest Consecutive Sequence

MEDIUM
10

Number of Good Ways to Split a String

MEDIUM
11

Number of Matching Subsequences

MEDIUM
12

Reorganize String

MEDIUM
13

Split Array into Consecutive Subsequences

MEDIUM

pattern 07

Prefix Sum

5 problems
1 easy4 medium
0 / 5 Solved
0%
01

Range Sum Query - Immutable

EASY
02

Contiguous Array

MEDIUM
03

Continuous Subarray Sum

MEDIUM
04

Subarray Sum Equals K

MEDIUM
05

Subarray Sums Divisible by K

MEDIUM

pattern 08

Two Pointers

5 problems
1 easy3 medium1 hard
0 / 5 Solved
0%
01

Merge Sorted Array

EASY
02

3Sum

MEDIUM
03

Container With Most Water

MEDIUM
04

Two Sum II - Input Array Is Sorted

MEDIUM
05

Trapping Rain Water

HARD

pattern 09

Fast and Slow Pointers

3 problems
2 easy1 medium
0 / 3 Solved
0%
01

Happy Number

EASY
02

Middle of the Linked List

EASY
03

Linked List Cycle II

MEDIUM

pattern 10

Sliding Window - Fixed Size

5 problems
1 easy3 medium1 hard
0 / 5 Solved
0%
01

Maximum Average Subarray I

EASY
02

Find All Anagrams in a String

MEDIUM
03

Maximum Sum of Distinct Subarrays With Length K

MEDIUM
04

Permutation in String

MEDIUM
05

Substring with Concatenation of All Words

HARD

pattern 11

Sliding Window - Dynamic Size

5 problems
4 medium1 hard
0 / 5 Solved
0%
01

Longest Repeating Character Replacement

MEDIUM
02

Longest Substring Without Repeating Characters

MEDIUM
03

Max Consecutive Ones III

MEDIUM
04

Minimum Size Subarray Sum

MEDIUM
05

Minimum Window Substring

HARD

pattern 12

Kadane's Algorithm

4 problems
4 medium
0 / 4 Solved
0%
01

Best Sightseeing Pair

MEDIUM
02

Maximum Product Subarray

MEDIUM
03

Maximum Subarray

MEDIUM
04

Maximum Sum Circular Subarray

MEDIUM

pattern 13

Recursion

3 problems
1 easy2 medium
0 / 3 Solved
0%
01

Merge Two Sorted Lists

EASY
02

Decode String

MEDIUM
03

Pow(x, n)

MEDIUM

pattern 14

Binary Search

10 problems
1 easy7 medium2 hard
0 / 10 Solved
0%
01

Search Insert Position

EASY
02

Find First and Last Position of Element in Sorted Array

MEDIUM
03

Find Minimum in Rotated Sorted Array

MEDIUM
04

Find Peak Element

MEDIUM
05

Koko Eating Bananas

MEDIUM
06

Random Pick with Weight

MEDIUM
07

Search a 2D Matrix

MEDIUM
08

Search in Rotated Sorted Array

MEDIUM
09

Find in Mountain Array

HARD
10

Median of Two Sorted Arrays

HARD

pattern 15

Bucket Sort

3 problems
3 medium
0 / 3 Solved
0%
01

Maximum Gap

MEDIUM
02

Sort Characters By Frequency

MEDIUM
03

Top K Frequent Words

MEDIUM

pattern 16

Merge Sort

2 problems
1 medium1 hard
0 / 2 Solved
0%
01

Sort List

MEDIUM
02

Reverse Pairs

HARD

pattern 17

QuickSort / QuickSelect

2 problems
2 medium
0 / 2 Solved
0%
01

Kth Largest Element in an Array

MEDIUM
02

Sort Colors

MEDIUM

pattern 18

Divide and Conquer

3 problems
3 medium
0 / 3 Solved
0%
01

Construct Quad Tree

MEDIUM
02

Convert Sorted List to Binary Search Tree

MEDIUM
03

Maximum Binary Tree

MEDIUM

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