A collection of Python DSA and SQL solutions organized for interview preparation.
Built to improve problem-solving skills, maintain consistency, and prepare for coding interviews.
Every problem here is chosen. Every solution is understood.
-- Solve 150+ quality DSA problems.
-- Complete LeetCode SQL 50.
-- Master pattern-based problem recognition.
-- Build strong problem-solving skills.
-- Strengthen SQL for interviews.
-- Maintain daily consistency.
-- Build a strong DSA foundation.
-- Crack placements & coding interviews.
Click any section to expand.
Python DSA
Arrays
Binary-Search
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 33 | Search in Rotated Sorted Array | Binary Search | O(log n) |
| 34 | Find First and Last Position of Element in Sorted Array | Binary Search | O(log n) |
| 35 | Search Insert Position | Binary Search | O(log n) |
| 69 | Sqrt(x) | Binary Search | O(log x) |
| 153 | Find Minimum in Rotated Sorted Array | Binary Search | O(log n) |
| 154 | Find Minimum in Rotated Sorted Array II | Binary Search | O(log n) avg |
| 405 | Convert a Number to Hexadecimal | Bit Manipulation / Number System | O(log n) |
| 3464 | Maximize the Distance Between Points on a Square | Binary Search / Geometry | O(n log n log P) |
Bit-Manipulation
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 136 | Single Number | Bit Manipulation / XOR | O(n) |
| 190 | Reverse Bits | Bit Manipulation | O(1) |
| 231 | Power of Two | Bit Manipulation | O(1) |
| 389 | Find the Difference | Bit Manipulation / XOR | O(n) |
| 3513 | Number of Unique XOR Triplets I | Bit Manipulation / Mathematics | O(1) |
| 3514 | Number of Unique XOR Triplets II | Bit Manipulation / Hash Set | O(u² + u × p) |
| 3702 | Longest Subsequence With Non-Zero Bitwise XOR | Bit Manipulation / XOR / Greedy | O(n) |
Dyanmc Programming
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 70 | Climbing Stairs | Fibonacci / DP | O(n) |
| 338 | Counting Bits | DP / Bit Manipulation | O(n) |
| 486 | Predict the Winner | Dynamic Programming / Game Theory | O(n²) |
| 877 | Stone Game | Dynamic Programming / Game Theory | O(n²) |
| 1140 | Stone Game II | Dynamic Programming / Game Theory / Memoization | O(n³) |
| 1301 | Number of Paths with Max Score | Dynamic Programming | O(n²) |
| 1320 | Minimum Distance to Type a Word Using Two Fingers | DP | O(26 * n) |
| 1340 | Jump Game V | DFS Memoization / DP | O(n * d) |
| 1406 | Stone Game III | Dynamic Programming / Game Theory | O(n) |
| 1510 | Stone Game IV | Dynamic Programming / Game Theory | O(n√n) |
| 1563 | Stone Game V | Dynamic Programming / Prefix Sum / Game Theory | O(n²) |
| 1871 | Jump Game VII | DP / Sliding Window | O(n) |
| 2463 | Minimum Total Distance Traveled | DP / Sorting | O(n * m * k) |
| 2770 | Maximum Number of Jumps to Reach the Last Index | Dynamic Programming | O(n^2) |
| 3225 | Maximum Score From Grid Operations | DP / Prefix Sum | O(n^3) |
| 3336 | Find the Number of Subsequences With Equal GCD | Dynamic Programming / GCD DP | O(n × S) |
| 3348 | Smallest Divisible Digit Product II | Dynamic Programming / Greedy / Mathematics | O(S + n) |
| 3418 | Maximum Amount of Money Robot Can Earn | Grid DP | O(m * n) |
| 3660 | Jump Game IX | DP / Prefix-Suffix | O(n) |
| 3661 | Maximum Walls Destroyed by Robots | DP / Memoization / Binary Search | O(n log m) |
| 3699 | Number of ZigZag Arrays I | Dynamic Programming | O(n × m) |
| 3700 | Number of ZigZag Arrays II | DP / Matrix Exponentiation | O((2m)^3 log n) |
| 3742 | Maximum Path Score in a Grid | Grid DP / Knapsack | O(m * n * k) |
Graphs
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 133 | Clone Graph | DFS / Hash Map | O(V + E) |
| 200 | Number of Islands | DFS / Matrix Traversal | O(m * n) |
| 695 | Max Area of Island | DFS / Matrix Traversal | O(m * n) |
| 1306 | Jump Game III | BFS / Graph Traversal | O(n) |
| 1345 | Jump Game IV | BFS / Graph Traversal | O(n) |
| 1391 | Check if There is a Valid Path in a Grid | BFS / Matrix Traversal | O(m * n) |
| 1559 | Detect Cycles in 2D Grid | DFS / Matrix Traversal | O(m * n) |
| 1722 | Minimize Hamming Distance After Swap Operations | Union Find / Hashing | O(n α(n)) |
| 2492 | Minimum Score of a Path Between Two Cities | DFS | O(n + m) |
| 2685 | Count the Number of Complete Components | Union Find (DSU) | O((n + m) · α(n)) |
| 2812 | Find the Safest Path in a Grid | Multi-Source BFS / Dijkstra | O(n² log n) |
| 3286 | Find a Safe Walk Through a Grid | Graphs / 0-1 BFS | O(m × n) |
| 3310 | Remove Methods From Project | Graph / BFS | O(n + m) |
| 3532 | Path Existence Queries in a Graph I | Connected Components | O(n + q) |
| 3534 | Path Existence Queries in a Graph II | Binary Lifting | O((n + q) log n) |
| 3620 | Network Recovery Pathways | Binary Search / DAG DP | O((n + m) log m) |
| 3629 | Minimum Jumps to Reach End via Prime Teleportation | BFS / Number Theory | O(n log log M) |
Greedy
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 45 | Jump Game II | Greedy | O(n) |
| 55 | Jump Game | Greedy | O(n) |
| 455 | Assign Cookies | Greedy / Two Pointers | O(n log n + m log m) |
| 561 | Array Partition | Greedy / Sorting | O(n log n) |
| 605 | Can Place Flowers | Greedy | O(n) |
| 976 | Largest Perimeter Triangle | Greedy / Sorting | O(n log n) |
| 1081 | Smallest Subsequence of Distinct Characters | Greedy / Monotonic Stack | O(n) |
| 1288 | Remove Covered Intervals | Greedy / Sorting | O(n log n) |
| 1665 | Minimum Initial Energy to Finish Tasks | Greedy / Sorting | O(n log n) |
| 1833 | Maximum Ice Cream Bars | Greedy / Sorting | O(n log n) |
| 1840 | Maximum Building Height | Greedy / Constraint Propagation | O(m log m) |
| 1846 | Maximum Element After Decreasing and Rearranging | Greedy / Sorting | O(n log n) |
| 2126 | Destroying Asteroids | Greedy / Sorting | O(n log n) |
| 2144 | Minimum Cost of Buying Candies With Discount | Greedy / Sorting | O(n log n) |
| 3014 | Minimum Number of Pushes to Type Word I | Greedy / Hash Map | O(n log n) |
| 3016 | Minimum Number of Pushes to Type Word II | Greedy / Frequency Counting | O(n) |
| 3302 | Find the Lexicographically Smallest Valid Sequence | Greedy / String Matching | O(n + m) |
| 3474 | Lexicographically Smallest Generated String | String Construction | O(n * m) |
| 3499 | Maximize Active Section with Trade I | Greedy / Strings | O(n) |
| 3501 | Maximize Active Section with Trade II | Greedy / Sparse Table / Binary Search | O(n log n + q log n) |
| 3633 | Earliest Finish Time for Land and Water Rides I | Greedy / Simulation | O(n * m) |
| 3635 | Earliest Finish Time for Land and Water Rides II | Greedy | O(n + m) |
| 3689 | Maximum Total Subarray Value I | Greedy / Math | O(n) |
| 3691 | Maximum Total Subarray Value II | Greedy / Heap / Sparse Table | O(n log n + k log k) |
Hashing
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 1 | Two Sum | HashMap Lookup | O(n) |
| 36 | Valid Sudoku | HashSet Validation | O(1) |
| 49 | Group Anagrams | HashMap + Sorted String | O(n log n) |
| 128 | Longest Consecutive Sequence | HashSet / Sequence Expansion | O(n) |
| 205 | Isomorphic Strings | Bi-directional HashMap | O(n) |
| 217 | Contains Duplicate | HashSet | O(n) |
| 219 | Contains Duplicate II | HashMap / Sliding Window | O(n) |
| 242 | Valid Anagram | Frequency Count | O(n) |
| 290 | Word Pattern | Bi-directional HashMap | O(n) |
| 347 | Top K Frequent Elements | Frequency Count / Bucket Sort | O(n) |
| 350 | Intersection of Two Arrays II | Hash Map / Counting | O(n + m) |
| 387 | First Unique Character in a String | Hash Map / Counting | O(n) |
| 451 | Sort Characters By Frequency | Frequency Count / Bucket Sort | O(n) |
| 454 | 4Sum II | Pair Sum + HashMap | O(n²) |
| 697 | Degree of an Array | Hash Map / Frequency Counting | O(n) |
| 874 | Walking Robot Simulation | Simulation / Hash Set | O(n + m) |
| 3020 | Find the Maximum Number of Elements in Subset | Hash Map / Greedy | O(n · log log M) |
| 3043 | Find the Length of the Longest Common Prefix | Hash Set / Prefix Matching | O((n+m) * d) |
| 3731 | Find Missing Elements | Hash Set | O(n + r) |
Linked List
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 2 | Add Two Numbers | Linked List | O(max(n,m)) |
| 21 | Merge Two Sorted Lists | Linked List / Two Pointers | O(n + m) |
| 61 | Rotate List | Two Pointers / Linked List | O(n) |
| 83 | Remove Duplicates from Sorted List | Linked List / Two Pointers | O(n) |
| 203 | Remove Linked List Elements | Linked List / Dummy Node | O(n) |
| 234 | Palindrome Linked List | Linked List / Fast & Slow Pointers | O(n) |
| 2095 | Delete the Middle Node of a Linked List | Fast & Slow Pointers | O(n) |
| 2130 | Maximum Twin Sum of a Linked List | Fast & Slow Pointers / Linked List Reversal | O(n) |
Math
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 7 | Reverse Integer | Number Manipulation | O(log n) |
| 9 | Palindrome Number | Number Manipulation | O(log n) |
| 168 | Excel Sheet Column Title | Mathematics / Base Conversion | O(log₍₂₆₎ n) |
| 171 | Excel Sheet Column Number | Mathematics / Base Conversion | O(n) |
| 202 | Happy Number | Math / Hash Set | O(log n) |
| 412 | Fizz Buzz | Simulation / Math | O(n) |
| 788 | Rotated Digits | Digit Check / Math | O(n * d) |
| 1344 | Angle Between Hands of a Clock | Math / Geometry | O(1) |
| 1523 | Count Odd Numbers in an Interval Range | Math | O(1) |
| 1979 | Find Greatest Common Divisor of Array | Mathematics / GCD | O(n + log(max(nums))) |
| 2029 | Stone Game IX | Game Theory / Mathematics / Modular Arithmetic | O(n) |
| 2520 | Count the Digits That Divide a Number | Number Manipulation | O(d) |
| 3312 | Sorted GCD Pair Queries | Number Theory / Inclusion-Exclusion | O(M log M + Q log M) |
| 3345 | Smallest Divisible Digit Product I | Mathematics / Brute Force | O(k × d) |
| 3536 | Maximum Product of Two Digits | Mathematics / Sorting | O(d log d) |
| 3653 | XOR After Range Multiplication Queries I | Simulation / Math | O(total updates) |
| 3655 | XOR After Range Multiplication Queries II | Math / Sqrt Decomposition | O(q * sqrt(n) + n * sqrt(n)) |
| 3658 | GCD of Odd and Even Sums | Mathematics / Number Theory | O(1) |
| 3751 | Total Waviness of Numbers in Range I | Math / Simulation | O((num2-num1) * D) |
| 3753 | Total Waviness of Numbers in Range II | Math / Digit DP / Counting | O(1) |
| 3783 | Mirror Distance of an Integer | Math | O(d) |
| 3867 | Sum of GCD of Formed Pairs | Mathematics / GCD / Sorting | O(n log n) |
| — | Sum of Primes Between Number and Its Reverse | Prime Checking | O(n√n) |
Prefix Sum
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 303 | Range Sum Query - Immutable | Prefix Sum | O(1) query |
| 560 | Subarray Sum Equals K | Prefix Sum + HashMap | O(n) |
| 1674 | Minimum Moves to Make Array Complementary | Prefix Sum / Sweep Line | O(n + limit) |
| 1732 | Find the Highest Altitude | Prefix Sum | O(n) |
| 2574 | Left and Right Sum Differences | Prefix Sum | O(n) |
| 2657 | Find the Prefix Common Array of Two Arrays | Hashing / Prefix | O(n) |
Sliding Window
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 3 | Longest Substring Without Repeating Characters | Sliding Window / Hash Set | O(n) |
| 1358 | Number of Substrings Containing All Three Characters | Sliding Window / Two Pointers | O(n) |
| 2958 | Length of Longest Subarray With at Most K Frequency | Sliding Window / Hash Map | O(n) |
| 3090 | Maximum Length Substring With Two Occurrences | Sliding Window / Hash Map | O(n) |
Stack
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 20 | Valid Parentheses | Stack | O(n) |
| 2751 | Robot Collisions | Stack / Simulation | O(n log n) |
Strings
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 5 | Longest Palindromic Substring | Expand Around Center | O(n^2) |
| 6 | Zigzag Conversion | Simulation / Strings | O(n) |
| 13 | Roman to Integer | Hashing / Strings | O(n) |
| 14 | Longest Common Prefix | Strings | O(S) |
| 28 | Find the Index of the First Occurrence in a String | Strings / Sliding Window | O((n-m+1)*m) |
| 58 | Length of Last Word | Strings | O(n) |
| 67 | Add Binary | Simulation / Strings | O(max(n,m)) |
| 345 | Reverse Vowels of a String | Strings / Two Pointers | O(n) |
| 409 | Longest Palindrome | Hashing / Strings | O(n) |
| 657 | Robot Return to Origin | Simulation | O(n) |
| 796 | Rotate String | Strings | O(n) |
| 1071 | Greatest Common Divisor of Strings | Strings / Mathematics | O(n + m) |
| 1189 | Maximum Number of Balloons | Hash Map / Counting | O(n) |
| 1768 | Merge Strings Alternately | Strings / Two Pointers | O(n + m) |
| 1967 | Number of Strings That Appear as Substrings in Word | Strings | O(n × m) |
| 2069 | Walking Robot Simulation II | Simulation / Design | O(1) |
| 2075 | Decode the Slanted Ciphertext | Matrix Traversal | O(n) |
| 2213 | Longest Substring of One Repeating Character | Segment Tree / String | O(n + q log n) |
| 2452 | Words Within Two Edits of Dictionary | Brute Force / Strings | O(q * d * L) |
| 2833 | Furthest Point From Origin | Counting / Strings | O(n) |
| 2840 | Check if Strings Can be Made Equal With Operations II | Even/Odd Index Grouping + Sorting | O(n log n) |
| 3093 | Longest Common Suffix Queries | Trie / Strings | O(total chars) |
| 3120 | Count the Number of Special Characters I | Hash Set / Strings | O(n) |
| 3121 | Count the Number of Special Characters II | Hashing / Strings | O(n) |
| 3517 | Smallest Palindromic Rearrangement I | Strings / Greedy / Hash Map | O(n + k log k) |
| 3518 | Smallest Palindromic Rearrangement II | Strings / Greedy / Combinatorics | O(n + m × k) |
| 3612 | Process String with Special Operations I | Simulation | O(n) |
| 3614 | Process String with Special Operations II | Reverse Simulation | O(n) |
| 3754 | Concatenate Non-Zero Digits and Multiply by Sum I | Strings / Simulation | O(d) |
| 3838 | Weighted Word Mapping | Strings / Simulation | O(n × m) |
Trees
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 2196 | Create Binary Tree From Descriptions | Trees / Hash Map | O(n) |
| 3161 | Block Placement Queries | Segment Tree / Sorted List | O(q log n) |
| 3558 | Number of Ways to Assign Edge Weights I | BFS / Combinatorics | O(n) |
| 3559 | Number of Ways to Assign Edge Weights II | LCA / Binary Lifting | O((n + q) log n) |
Two Pointers
| # | Problem | Pattern | Complexity |
|---|---|---|---|
| 11 | Container With Most Water | Opposite Ends Two Pointers | O(n) |
| 15 | 3Sum | Sorting + Two Pointers | O(n²) |
| 16 | 3Sum Closest | Sorting + Two Pointers | O(n²) |
| 18 | 4Sum | Two Pointers / Sorting | O(n^3) |
| 26 | Remove Duplicates from Sorted Array | Slow / Fast Pointer | O(n) |
| 42 | Trapping Rain Water | Two Pointers + Left/Right Max | O(n) |
| 88 | Merge Sorted Array | Three Pointers (Backwards Merge) | O(n) |
| 125 | Valid Palindrome | Inward Two Pointers | O(n) |
| 167 | Two Sum II | Sorted Two Pointers | O(n) |
| 283 | Move Zeroes | Slow / Fast Pointer | O(n) |
| 344 | Reverse String | Opposite Ends Two Pointers | O(n) |
| 392 | Is Subsequence | Two Pointers / Greedy | O(n) |
| 977 | Squares of a Sorted Array | Opposite Ends Two Pointers | O(n) |
| 1855 | Maximum Distance Between a Pair of Values | Two Pointers | O(n + m) |
| 2540 | Minimum Common Value | Two Pointers | O(n + m) |
| 3756 | Concatenate Non-Zero Digits and Multiply by Sum II | Prefix Sum / Prefix Processing | O(n + q) |
SQL
Easy
| ID | Problem | Topic | Difficulty |
|---|---|---|---|
| 181 | Employees Earning More Than Their Managers | Self JOIN | Easy |
| 182 | Duplicate Emails | GROUP BY / HAVING | Easy |
| 183 | Customers Who Never Order | LEFT JOIN | Easy |
| 196 | Delete Duplicate Emails | DELETE / SELF JOIN | Easy |
| 197 | Rising Temperature | SELF JOIN | Easy |
| 577 | Employee Bonus | LEFT JOIN / Filtering | Easy |
| 584 | Find Customer Referee | Filtering / NULL Handling | Easy |
| 586 | Customer Placing the Largest Number of Orders | SQL / GROUP BY / Aggregate Functions | O(n) |
| 595 | Big Countries | Filtering | Easy |
| 596 | Classes With at Least 5 Students | GROUP BY / HAVING | Easy |
| 607 | Sales Person | SQL / Subquery / JOIN / NOT IN | Easy |
| 610 | Triangle Judgement | CASE WHEN | Easy |
| 619 | Biggest Single Number | GROUP BY / HAVING | Easy |
| 620 | Not Boring Movies | Filtering / ORDER BY | Easy |
| 627 | Swap Sex of Employees | SQL / UPDATE / Conditional Function | Easy |
| 1050 | Actors and Directors Who Cooperated At Least Three Times | SQL / GROUP BY / HAVING | Easy |
| 1068 | Product Sales Analysis I | INNER JOIN | Easy |
| 1075 | Project Employees I | JOIN / GROUP BY / AVG | Easy |
| 1141 | User Activity for the Past 30 Days I | GROUP BY / COUNT DISTINCT | Easy |
| 1148 | Article Views I | Filtering / DISTINCT | Easy |
| 1211 | Queries Quality and Percentage | GROUP BY / Aggregation | Easy |
| 1251 | Average Selling Price | JOIN / Aggregation | Easy |
| 1280 | Students and Examinations | CROSS JOIN / LEFT JOIN / GROUP BY | Easy |
| 1327 | List the Products Ordered in a Period | JOIN / GROUP BY | Easy |
| 1378 | Replace Employee ID With The Unique Identifier | LEFT JOIN | Easy |
| 1407 | Top Travellers | SQL / LEFT JOIN / GROUP BY / Aggregate Functions | Easy |
| 1484 | Group Sold Products By The Date | GROUP BY / String Aggregation | Easy |
| 1517 | Find Users With Valid E-Mails | Regular Expressions | Easy |
| 1527 | Patients With a Condition | String Matching | Easy |
| 1581 | Customer Who Visited but Did Not Make Any Transactions | LEFT JOIN / GROUP BY | Easy |
| 1633 | Percentage of Users Attended a Contest | GROUP BY / Aggregation | Easy |
| 1661 | Average Time of Process per Machine | SELF JOIN / GROUP BY | Easy |
| 1667 | Fix Names in a Table | String Functions | Easy |
| 1683 | Invalid Tweets | String Functions / Filtering | Easy |
| 1693 | Daily Leads and Partners | SQL / GROUP BY / COUNT DISTINCT | Easy |
| 1729 | Find Followers Count | GROUP BY / COUNT | Easy |
| 1757 | Recyclable and Low Fat Products | Filtering | Easy |
| 1978 | Employees Whose Manager Left the Company | Subquery / Filtering | Easy |
| 2356 | Number of Unique Subjects Taught by Each Teacher | GROUP BY / COUNT DISTINCT | Easy |
Medium
| ID | Problem | Topic | Difficulty |
|---|---|---|---|
| 176 | Second Highest Salary | Subquery / DISTINCT | Medium |
| 180 | Consecutive Numbers | SELF JOIN | Medium |
| 550 | Game Play Analysis IV | JOIN / Conditional Aggregation | Medium |
| 570 | Managers with at Least 5 Direct Reports | SELF JOIN / GROUP BY | Medium |
| 585 | Investments in 2016 | GROUP BY / Subquery | Medium |
| 602 | Friend Requests II: Who Has the Most Friends | UNION ALL / GROUP BY | Medium |
| 626 | Exchange Seats | CASE WHEN | Medium |
| 1045 | Customers Who Bought All Products | GROUP BY / HAVING / COUNT DISTINCT | Medium |
| 1070 | Product Sales Analysis III | GROUP BY / JOIN | Medium |
| 1164 | Product Price at a Given Date | GROUP BY / LEFT JOIN | Medium |
| 1174 | Immediate Food Delivery II | GROUP BY / Conditional Aggregation | Medium |
| 1193 | Monthly Transactions I | GROUP BY / Conditional Aggregation | Medium |
| 1204 | Last Person to Fit in the Bus | Window Function / Running Sum | Medium |
| 1321 | Restaurant Growth | Window Function / Rolling Average | Medium |
| 1341 | Movie Rating | JOIN / GROUP BY / Aggregation | Medium |
| 1731 | The Number of Employees Which Report to Each Employee | SELF JOIN / GROUP BY | Medium |
| 1789 | Primary Department for Each Employee | Filtering / GROUP BY | Medium |
| 1907 | Count Salary Categories | CASE WHEN / Aggregation | Medium |
| 1934 | Confirmation Rate | LEFT JOIN / GROUP BY / Conditional Aggregation | Medium |
Hard
| ID | Problem | Topic | Difficulty |
|---|---|---|---|
| 185 | Department Top Three Salaries | Window Function / DENSE_RANK | Hard |
Pandas
| ID | Problem | Topic | Complexity |
|---|---|---|---|
| 1873 | Calculate Special Bonus | Conditional Selection | O(n) |
| 2877 | Create a DataFrame from List | DataFrame Creation | O(n) |
| 2878 | Get the Size of a DataFrame | DataFrame Properties | O(1) |
| 2879 | Display the First Three Rows | DataFrame Selection | O(1) |
| 2880 | Select Data | DataFrame Selection | O(1) |
| 2881 | Create a New Column | Column Operations | O(n) |
| 2882 | Drop Duplicate Rows | Data Cleaning | O(n) |
| 2883 | Drop Missing Data | Data Cleaning | O(n) |
| 2884 | Modify Columns | Column Operations | O(n) |
| 2885 | Rename Columns | DataFrame Operations | O(1) |
| 2886 | Change Data Type | Data Type Conversion | O(n) |
| 2887 | Fill Missing Data | Missing Data Handling | O(n) |
| 2888 | Reshape Data: Concatenate | DataFrame Reshaping | O(n + m) |
| 2889 | Reshape Data: Pivot | DataFrame Reshaping | O(n) |
| 2890 | Reshape Data: Melt | DataFrame Reshaping | O(n) |
| 2891 | Method Chaining | Method Chaining | O(n) |
"A mediocre solution you understand beats a perfect solution you copied."
The goal isn't to solve 500 problems blindly.
The goal is to see a new problem and know which pattern it belongs to — in under 30 seconds.
If this repo helped you, drop a ⭐ — it keeps the daily streak going.
This repository is updated daily as I grind pattern by pattern.