DSA Tracker

146 problems, by pattern

Your curated set. Solve on LeetCode, tick it here. When LeetCode sync is on, solves tick themselves.

Arrays

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Two Sum

Easy · Hash map complement

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Best Time to Buy and Sell Stock

Easy · Track running min

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Contains Duplicate

Easy · Set membership

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Product of Array Except Self

Medium · Prefix/suffix products

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Maximum Subarray

Medium · Kadane's

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Maximum Product Subarray

Medium · Track min & max

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Merge Intervals

Medium · Sort + sweep

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Insert Interval

Medium · Interval merge

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Rotate Array

Medium · Reverse trick

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Set Matrix Zeroes

Medium · In-place markers

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Strings

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Valid Anagram

Easy · Char counts

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Valid Palindrome

Easy · Two pointers

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Longest Common Prefix

Easy · Vertical scan

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Reverse String

Easy · Two pointers in place

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Longest Palindromic Substring

Medium · Expand around center

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Palindromic Substrings

Medium · Expand around center

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Group Anagrams

Medium · Hash by sorted key

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Encode and Decode Strings

Medium · Length prefixing

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String to Integer (atoi)

Medium · Careful parsing

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Zigzag Conversion

Medium · Simulation

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Hashing

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Top K Frequent Elements

Medium · Bucket sort

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Valid Sudoku

Medium · Sets per unit

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Longest Consecutive Sequence

Medium · Set + sequence start

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Subarray Sum Equals K

Medium · Prefix sum + map

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Ransom Note

Easy · Char counts

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First Unique Character in a String

Easy · Frequency map

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Intersection of Two Arrays

Easy · Set intersection

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4Sum II

Medium · Pair-sum map

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LRU Cache

Medium · Hash + doubly linked list

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Insert Delete GetRandom O(1)

Medium · Map + array swap

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Two Pointers

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Two Sum II - Input Array Is Sorted

Medium · Converging pointers

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3Sum

Medium · Sort + two pointers

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Container With Most Water

Medium · Greedy shrink

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Trapping Rain Water

Hard · Two pointers + max

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Remove Duplicates from Sorted Array

Easy · Slow/fast

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Move Zeroes

Easy · Slow/fast

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Sort Colors

Medium · Dutch national flag

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3Sum Closest

Medium · Sort + two pointers

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Boats to Save People

Medium · Greedy pairing

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Is Subsequence

Easy · Two pointers

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Sliding Window

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Longest Substring Without Repeating Characters

Medium · Window + set

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Longest Repeating Character Replacement

Medium · Window + max freq

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Permutation in String

Medium · Fixed window counts

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Minimum Window Substring

Hard · Shrinking window

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Sliding Window Maximum

Hard · Monotonic deque

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Maximum Average Subarray I

Easy · Fixed window sum

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Minimum Size Subarray Sum

Medium · Shrinking window

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Fruit Into Baskets

Medium · Window of 2 types

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Max Consecutive Ones III

Medium · Window with k flips

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Find All Anagrams in a String

Medium · Fixed window counts

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Sorting

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Merge Sorted Array

Easy · Merge from back

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Sort an Array

Medium · Merge/quick sort

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Kth Largest Element in an Array

Medium · Quickselect

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Sort Characters By Frequency

Medium · Count + sort

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Largest Number

Medium · Custom comparator

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H-Index

Medium · Sort + count

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Meeting Rooms

Easy · Sort intervals

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Meeting Rooms II

Medium · Sort + min-heap

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Non-overlapping Intervals

Medium · Greedy by end

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Car Fleet

Medium · Sort + monotonic stack

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Binary Search

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Binary Search

Easy · Classic

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Search Insert Position

Easy · Lower bound

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Search a 2D Matrix

Medium · Flattened binary search

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Koko Eating Bananas

Medium · Search on answer

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Find Minimum in Rotated Sorted Array

Medium · Pivot search

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Search in Rotated Sorted Array

Medium · Pivot search

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Time Based Key-Value Store

Medium · Binary search on time

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Median of Two Sorted Arrays

Hard · Partition search

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Find First and Last Position

Medium · Lower/upper bound

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Capacity To Ship Packages Within D Days

Medium · Search on answer

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Linked List

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Reverse Linked List

Easy · Pointer flipping

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Merge Two Sorted Lists

Easy · Merge with dummy

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Linked List Cycle

Easy · Floyd's tortoise/hare

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Reorder List

Medium · Find mid + reverse + merge

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Remove Nth Node From End of List

Medium · Two pointers gap

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Copy List with Random Pointer

Medium · Interleave clone

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Add Two Numbers

Medium · Digit carry

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Find the Duplicate Number

Medium · Cycle detection

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Merge k Sorted Lists

Hard · Min-heap merge

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Reverse Nodes in k-Group

Hard · Group reversal

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Stack

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Valid Parentheses

Easy · Matching stack

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Min Stack

Medium · Track min per push

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Evaluate Reverse Polish Notation

Medium · Operand stack

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Generate Parentheses

Medium · Backtracking + stack

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Daily Temperatures

Medium · Monotonic stack

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Largest Rectangle in Histogram

Hard · Monotonic stack

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Next Greater Element I

Easy · Monotonic stack

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Asteroid Collision

Medium · Simulation stack

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Decode String

Medium · Nested stack

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Simplify Path

Medium · Path stack

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Queue

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Implement Stack using Queues

Easy · Queue rotation

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Implement Queue using Stacks

Easy · Two stacks

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Number of Recent Calls

Easy · Sliding queue

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Design Circular Queue

Medium · Ring buffer

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Moving Average from Data Stream

Easy · Fixed window queue

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Dota2 Senate

Medium · Two queues

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Task Scheduler

Medium · Greedy + queue

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Rotting Oranges

Medium · Multi-source BFS

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Walls and Gates

Medium · Multi-source BFS

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Open the Lock

Medium · BFS on states

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Trees

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Invert Binary Tree

Easy · Recursion

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Maximum Depth of Binary Tree

Easy · DFS depth

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Diameter of Binary Tree

Easy · DFS + global max

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Balanced Binary Tree

Easy · DFS height check

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Same Tree

Easy · Parallel DFS

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Subtree of Another Tree

Easy · DFS + compare

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Binary Tree Level Order Traversal

Medium · BFS by level

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Binary Tree Right Side View

Medium · BFS last per level

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Lowest Common Ancestor of a Binary Tree

Medium · DFS return

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Binary Tree Maximum Path Sum

Hard · DFS + global max

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BST

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Lowest Common Ancestor of a BST

Medium · BST property

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Validate Binary Search Tree

Medium · Range bounds

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Kth Smallest Element in a BST

Medium · Inorder traversal

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Convert Sorted Array to BST

Easy · Divide + conquer

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Insert into a BST

Medium · BST insert

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Delete Node in a BST

Medium · BST delete

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Range Sum of BST

Easy · Pruned DFS

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Minimum Absolute Difference in BST

Easy · Inorder diff

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Binary Search Tree Iterator

Medium · Controlled inorder

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Construct Binary Tree from Preorder and Inorder

Medium · Recursive build

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Heap

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Kth Largest Element in a Stream

Easy · Min-heap of size k

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Last Stone Weight

Easy · Max-heap

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K Closest Points to Origin

Medium · Heap by distance

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Top K Frequent Words

Medium · Heap with comparator

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Find Median from Data Stream

Hard · Two heaps

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Reorganize String

Medium · Greedy max-heap

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Design Twitter

Medium · Heap merge feeds

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Least Number of Unique Integers after K Removals

Medium · Freq + heap

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Single-Threaded CPU

Medium · Sort + heap

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Maximum Subsequence Score

Medium · Sort + min-heap

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Graphs

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Number of Islands

Medium · Flood fill DFS/BFS

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Clone Graph

Medium · DFS + hash map

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Course Schedule

Medium · Topological sort

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Pacific Atlantic Water Flow

Medium · Multi-source DFS

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Max Area of Island

Medium · Flood fill + count

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Graph Valid Tree

Medium · Union-find

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Number of Connected Components

Medium · Union-find

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Word Ladder

Hard · BFS shortest path

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Dynamic Programming

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Climbing Stairs

Easy · 1D DP (Fibonacci)

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House Robber

Medium · 1D DP choice

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Coin Change

Medium · Unbounded knapsack

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Longest Increasing Subsequence

Medium · DP / patience

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Longest Common Subsequence

Medium · 2D DP

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Word Break

Medium · DP over string

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Unique Paths

Medium · 2D grid DP

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Edit Distance

Medium · 2D DP

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