Is Skill Shiksha coding practice free?

Yes. You can read every problem for free, and a free account lets you run your code, submit solutions, earn XP, keep a daily streak and appear on the leaderboard.

Which programming languages can I use?

You can write and run solutions in JavaScript, Python, Java, C++, Kotlin and Dart, directly in the browser. No setup or installation is needed.

How many problems are there and which topics do they cover?

There are 177 problems across 20 topics: Basics, Arrays, Strings, Hashing, Two Pointers, Sliding Window, Binary Search, Linked List, Stack & Queue, Recursion & Backtracking, Greedy, Heap, Trees, Tries, Graphs, Dynamic Programming, Bit Manipulation, Math, Intervals, Design. Every topic has Easy, Medium and Hard problems so you can build up from basics to interview level.

Where should I start if I am preparing for coding interviews?

Start with the Interview Core sheet. It covers every common interview pattern in a learning order. Beginners can warm up with the Skill Shiksha Starter sheet, and the SDE, Blind 75 and Pattern sheets give more practice per topic.

How are my solutions checked?

Your code runs against hidden test cases and you get a verdict such as Accepted, Wrong Answer, Time Limit Exceeded or Runtime Error. Sample cases show your output next to the expected output so you can debug. You can also run your own custom input.

How do XP, levels and streaks work?

Your first accepted solution for each problem earns XP: 10 for Easy, 25 for Medium and 50 for Hard. XP raises your level. Solving at least one problem a day keeps your streak alive, and badges unlock as you reach milestones.

Can I see the official solution?

Yes. The official solution, with the approach and its time and space complexity, unlocks after you solve a problem or after three attempts. Three progressive hints are available before that.

Coding Practice

Learn the patterns behind interview questions. Write code in your browser, run it against real test cases, unlock hints, and watch your streak grow.

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Daily challenge

First and Last Position of Element

MediumBinary Search +25 XP

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Study sheets

Follow a guided path, topic by topic.

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All problems

177 problems

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Showing 177 of 177

Not started1.Sum of Two NumbersBasicsEasy
Not started2.Even or OddBasicsEasy
Not started3.FizzBuzzBasicsEasy
Not started4.FactorialBasicsEasy
Not started5.Sum of DigitsBasicsEasy
Not started6.Check PrimeBasicsEasy
Not started7.Fibonacci NumberBasicsEasy
Not started8.Largest and Smallest in ArrayBasicsEasy
Not started9.Reverse a StringBasicsEasy
Not started10.Move ZeroesArraysEasy
Not started11.Best Time to Buy and Sell StockArraysEasy
Not started12.Majority ElementArraysEasy
Not started13.Sort ColorsArraysMedium
Not started14.Find the Duplicate NumberArraysMedium
Not started15.Maximum SubarrayArraysMedium
Not started16.Next PermutationArraysMedium
Not started17.Product of Array Except SelfArraysMedium
Not started18.Maximum Product SubarrayArraysMedium
Not started19.Set Matrix ZeroesArraysMedium
Not started20.Rotate ImageArraysMedium
Not started21.Spiral MatrixArraysMedium
Not started22.Rotate ArrayArraysMedium
Not started23.Count InversionsArraysHard
Not started24.First Missing PositiveArraysHard
Not started25.Valid PalindromeStringsEasy
Not started26.Valid AnagramStringsEasy
Not started27.Find the Index of the First Occurrence in a StringStringsEasy
Not started28.Reverse Words in a StringStringsMedium
Not started29.Group AnagramsStringsMedium
Not started30.Longest Palindromic SubstringStringsMedium
Not started31.Palindromic SubstringsStringsMedium
Not started32.String to Integer (atoi)StringsMedium
Not started33.Shortest PalindromeStringsHard
Not started34.Two SumHashingEasy
Not started35.Contains DuplicateHashingEasy
Not started36.Longest Consecutive SequenceHashingMedium
Not started37.Subarray Sum Equals KHashingMedium
Not started38.Contiguous ArrayHashingMedium
Not started39.Max Points on a LineHashingHard
Not started40.Squares of a Sorted ArrayTwo PointersEasy
Not started41.Two Sum II - Sorted ArrayTwo PointersMedium
Not started42.Container With Most WaterTwo PointersMedium
Not started43.3SumTwo PointersMedium
Not started44.Trapping Rain WaterTwo PointersHard
Not started45.Maximum Sum Subarray of Size KSliding WindowEasy
Not started46.Longest Substring Without Repeating CharactersSliding WindowMedium
Not started47.Longest Repeating Character ReplacementSliding WindowMedium
Not started48.Permutation in StringSliding WindowMedium
Not started49.Minimum Size Subarray SumSliding WindowMedium
Not started50.Minimum Window SubstringSliding WindowHard
Not started51.Sliding Window MaximumSliding WindowHard
Not started52.Binary SearchBinary SearchEasy
Not started53.Search Insert PositionBinary SearchEasy
Not started54.Integer Square RootBinary SearchEasy
Not started55.First and Last Position of ElementBinary SearchMedium
Not started56.Search in Rotated Sorted ArrayBinary SearchMedium
Not started57.Find Minimum in Rotated Sorted ArrayBinary SearchMedium
Not started58.Search a 2D MatrixBinary SearchMedium
Not started59.Koko Eating BananasBinary SearchMedium
Not started60.Aggressive CowsBinary SearchMedium
Not started61.Peak Index in a Mountain ArrayBinary SearchMedium
Not started62.Split Array Largest SumBinary SearchHard
Not started63.Median of Two Sorted ArraysBinary SearchHard
Not started64.Reverse Linked ListLinked ListEasy
Not started65.Merge Two Sorted ListsLinked ListEasy
Not started66.Linked List CycleLinked ListEasy
Not started67.Palindrome Linked ListLinked ListEasy
Not started68.Remove Nth Node From End of ListLinked ListMedium
Not started69.Add Two NumbersLinked ListMedium
Not started70.Reorder ListLinked ListMedium
Not started71.Sort ListLinked ListMedium
Not started72.Reverse Linked List IILinked ListMedium
Not started73.Merge K Sorted ListsLinked ListHard
Not started74.Reverse Nodes in k-GroupLinked ListHard
Not started75.Valid ParenthesesStack & QueueEasy
Not started76.Implement Queue using StacksStack & QueueEasy
Not started77.Min StackStack & QueueMedium
Not started78.Evaluate Reverse Polish NotationStack & QueueMedium
Not started79.Daily TemperaturesStack & QueueMedium
Not started80.Decode StringStack & QueueMedium
Not started81.Asteroid CollisionStack & QueueMedium
Not started82.Largest Rectangle in HistogramStack & QueueHard
Not started83.Basic CalculatorStack & QueueHard
Not started84.Binary Strings of Length NRecursion & BacktrackingEasy
Not started85.SubsetsRecursion & BacktrackingMedium
Not started86.Combination SumRecursion & BacktrackingMedium
Not started87.Combination Sum IIRecursion & BacktrackingMedium
Not started88.PermutationsRecursion & BacktrackingMedium
Not started89.Letter Combinations of a Phone NumberRecursion & BacktrackingMedium
Not started90.Generate ParenthesesRecursion & BacktrackingMedium
Not started91.Palindrome PartitioningRecursion & BacktrackingMedium
Not started92.Word SearchRecursion & BacktrackingMedium
Not started93.N-QueensRecursion & BacktrackingHard
Not started94.Assign CookiesGreedyEasy
Not started95.Best Time to Buy and Sell Stock IIGreedyMedium
Not started96.Jump GameGreedyMedium
Not started97.Jump Game IIGreedyMedium
Not started98.Gas StationGreedyMedium
Not started99.Partition LabelsGreedyMedium
Not started100.CandyGreedyHard
Not started101.Last Stone WeightHeapEasy
Not started102.Kth Largest Element in an ArrayHeapMedium
Not started103.Top K Frequent ElementsHeapMedium
Not started104.K Closest Points to OriginHeapMedium
Not started105.Task SchedulerHeapMedium
Not started106.Find Median from Data StreamHeapHard
Not started107.Maximum Depth of Binary TreeTreesEasy
Not started108.Invert Binary TreeTreesEasy
Not started109.Symmetric TreeTreesEasy
Not started110.Diameter of Binary TreeTreesEasy
Not started111.Binary Tree Inorder TraversalTreesEasy
Not started112.Binary Tree Level Order TraversalTreesMedium
Not started113.Binary Tree Right Side ViewTreesMedium
Not started114.Validate Binary Search TreeTreesMedium
Not started115.Kth Smallest Element in a BSTTreesMedium
Not started116.Lowest Common Ancestor of a Binary TreeTreesMedium
Not started117.Construct Binary Tree from Preorder and Inorder TraversalTreesMedium
Not started118.Path Sum IIITreesMedium
Not started119.Binary Tree Maximum Path SumTreesHard
Not started120.Vertical Order Traversal of a Binary TreeTreesHard
Not started121.Count Words With a Given PrefixTriesEasy
Not started122.Implement Trie (Prefix Tree)TriesMedium
Not started123.Design Add and Search Words Data StructureTriesMedium
Not started124.Word Search IITriesHard
Not started125.Flood FillGraphsEasy
Not started126.Number of IslandsGraphsMedium
Not started127.Rotting OrangesGraphsMedium
Not started128.Pacific Atlantic Water FlowGraphsMedium
Not started129.Number of ProvincesGraphsMedium
Not started130.Course ScheduleGraphsMedium
Not started131.Is Graph BipartiteGraphsMedium
Not started132.Network Delay TimeGraphsMedium
Not started133.Cheapest Flights Within K StopsGraphsMedium
Not started134.Minimum Spanning TreeGraphsMedium
Not started135.Redundant ConnectionGraphsMedium
Not started136.Word LadderGraphsHard
Not started137.Alien DictionaryGraphsHard
Not started138.Climbing StairsDynamic ProgrammingEasy
Not started139.House RobberDynamic ProgrammingMedium
Not started140.House Robber IIDynamic ProgrammingMedium
Not started141.Decode WaysDynamic ProgrammingMedium
Not started142.Coin ChangeDynamic ProgrammingMedium
Not started143.Coin Change IIDynamic ProgrammingMedium
Not started144.Longest Increasing SubsequenceDynamic ProgrammingMedium
Not started145.Longest Common SubsequenceDynamic ProgrammingMedium
Not started146.0/1 KnapsackDynamic ProgrammingMedium
Not started147.Unique PathsDynamic ProgrammingMedium
Not started148.Partition Equal Subset SumDynamic ProgrammingMedium
Not started149.Word BreakDynamic ProgrammingMedium
Not started150.Best Time to Buy and Sell Stock with CooldownDynamic ProgrammingMedium
Not started151.Edit DistanceDynamic ProgrammingHard
Not started152.Regular Expression MatchingDynamic ProgrammingHard
Not started153.Burst BalloonsDynamic ProgrammingHard
Not started154.Single NumberBit ManipulationEasy
Not started155.Number of 1 BitsBit ManipulationEasy
Not started156.Counting BitsBit ManipulationEasy
Not started157.Missing NumberBit ManipulationEasy
Not started158.Single Number IIBit ManipulationMedium
Not started159.Sum of Two IntegersBit ManipulationMedium
Not started160.Count Total Set BitsBit ManipulationHard
Not started161.GCD and LCMMathEasy
Not started162.Happy NumberMathEasy
Not started163.Factorial Trailing ZeroesMathEasy
Not started164.Count PrimesMathMedium
Not started165.Modular ExponentiationMathMedium
Not started166.Multiply StringsMathMedium
Not started167.Nth Fibonacci ModuloMathHard
Not started168.Meeting RoomsIntervalsEasy
Not started169.Merge IntervalsIntervalsMedium
Not started170.Insert IntervalIntervalsMedium
Not started171.Non-overlapping IntervalsIntervalsMedium
Not started172.Meeting Rooms IIIntervalsMedium
Not started173.Employee Free TimeIntervalsHard
Not started174.Implement Stack using QueuesDesignEasy
Not started175.LRU CacheDesignMedium
Not started176.Time Based Key-Value StoreDesignMedium
Not started177.LFU CacheDesignHard

Coding Practice

Solve one problem a day. Build the habit.

First and Last Position of Element

Study sheets

Interview Core

Skill Shiksha Starter

Skill Shiksha SDE Sheet

Blind 75

Skill Shiksha Pattern Sheet

All problems

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