#1
EasyTwo Sum
Hash map lookupFoundationalMust do
The cleanest warm-up for complements, maps, and one-pass reasoning.
Common OA opener across product and service companies.
ArrayHash Table
Placements 2026
DSA Sheet 2026 for internships, placements, and calm revision.
This is not a giant dump of random questions. It is the shortlist I would actually use if I had to prepare again for 2026 hiring cycles in India: high-yield patterns, interview-friendly sequencing, and direct links to the internal write-ups on this site.
54curated problems
8pattern sections
0 fluffjust the repeatable shortlist
How to use this sheet
Start with foundational items, then move to the high-priority mediums, then revisit the capstones in timed rounds. Every card below pushes you first to the internal explanation, then to the original problem for practice.
What is deliberately not in MVP 1
No fake locked dashboards, no auth wall, no half-baked online judge. The first version is about useful content, clear progression, and a recurring traffic base we can grow into progress tracking later.
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Pattern track
Back to topArrays and Hashing
These are the fastest wins for online assessments. Nail lookup trade-offs, prefix-style thinking, and interval manipulation first.
#121
EasyBest Time to Buy and Sell Stock
Running minimumFoundationalMust do
Teaches you to maintain the best state so far without nested loops.
Very common in internship screens and early phone rounds.
ArrayDynamic Programming
#217
EasyContains Duplicate
Set membershipFoundational
Simple on purpose. Interviewers use it to test baseline coding speed.
Frequent warm-up or OA filler question.
ArrayHash TableSorting
#238
MediumProduct of Array Except Self
Prefix and suffix productsHighMust do
Forces you to reason about state carried from both directions.
Popular when interviewers want more than brute force arrays.
ArrayPrefix Sum
#53
MediumMaximum Subarray
Kadane’s algorithmHighMust do
A classic recurrence that shows up in many disguised DP problems.
A staple across placements and mid-level interviews.
ArrayDynamic ProgrammingDivide and Conquer
#347
MediumTop K Frequent Elements
Bucket sort on frequenciesHigh
Great for frequency counting plus output-size-aware optimization.
Common when interviewers want hash map plus heap alternatives.
ArrayHash TableBucket SortHeap
#56
MediumMerge Intervals
Sort and mergeHighMust do
Intervals are everywhere in placements. This is the base pattern.
Shows up often in Amazon-style interview prep lists.
ArraySortingIntervals
#57
MediumInsert Interval
Intervals with splice logicHigh
Builds on merge intervals and checks implementation discipline.
Good follow-up after interval basics.
ArrayIntervals
Pattern track
Back to topStrings and Sliding Window
This section is high-yield for OAs because it rewards pattern recognition more than heavy theory.
#125
EasyValid Palindrome
Two pointersFoundational
Tests edge-case handling and pointer movement on noisy input.
Very common in short screening rounds.
Two PointersString
#14
EasyLongest Common Prefix
Horizontal scanningFoundational
Short problem that reveals code clarity and string handling.
Frequent easy string question.
StringTrie
#49
MediumGroup Anagrams
Canonical signature mappingHighMust do
Useful for grouping and normalization problems.
Common OA and interview favorite.
ArrayHash TableStringSorting
#3
MediumLongest Substring Without Repeating Characters
Dynamic sliding windowFoundationalMust do
Probably the most important sliding-window problem to internalize.
Appears everywhere from internships to experienced hiring.
Hash TableStringSliding Window
#424
MediumLongest Repeating Character Replacement
Window with best-frequency invariantHigh
Teaches when a slightly stale invariant is still valid and efficient.
Excellent differentiator question in placements.
Hash TableStringSliding Window
#567
MediumPermutation in String
Fixed-size frequency windowHigh
Builds confidence with character counts and rolling comparisons.
Frequently appears in OA practice sheets.
Hash TableTwo PointersStringSliding Window
#76
HardMinimum Window Substring
Variable-size minimum valid windowCapstoneMust do
The capstone sliding-window problem for interview prep.
A strong signal question in top-company rounds.
Hash TableStringSliding Window
#11
MediumContainer With Most Water
Greedy two pointersHigh
Sharpens elimination reasoning instead of brute-force pair checks.
Common in interview prep sheets due to elegant reasoning.
ArrayTwo PointersGreedy
Pattern track
Back to topLinked List
Placements love linked lists because they expose pointer confidence fast. If this feels slow, practice until it feels mechanical.
#206
EasyReverse Linked List
Pointer reversalFoundationalMust do
The most reusable linked-list primitive by far.
One of the most frequently asked linked-list questions.
Linked ListRecursion
#141
EasyLinked List Cycle
Fast and slow pointersFoundationalMust do
Introduces Floyd cycle detection, which keeps showing up later.
Classic interview question across levels.
Hash TableLinked ListTwo Pointers
#21
EasyMerge Two Sorted Lists
Dummy node mergeFoundational
A good test of clean pointer manipulation and base cases.
Common easy-to-medium linked-list question.
Linked ListRecursion
#19
MediumRemove Nth Node From End of List
Gap two-pointer techniqueHigh
A compact way to practice offsets and dummy heads.
Popular because the one-pass solution is memorable.
Linked ListTwo Pointers
#2
MediumAdd Two Numbers
Digit-wise carry simulationHigh
Checks if you can combine arithmetic state with list traversal.
Very common question bank entry.
Linked ListMathRecursion
#143
MediumReorder List
Split, reverse, weaveCapstoneMust do
A great capstone because it combines three linked-list patterns.
Strong medium question for campus interviews.
Linked ListTwo PointersStackRecursion
Pattern track
Back to topStack and Queue
These questions reward composure. Interviewers often use them to see if you can model state transitions clearly.
#20
EasyValid Parentheses
Matching stackFoundational
Basic stack fluency. Solve this fast and flawlessly.
Very common opening stack question.
StringStack
#155
MediumMin Stack
Auxiliary state stackHigh
Shows how to augment a basic data structure with cached answers.
Frequent object-design style interview question.
StackDesign
#150
MediumEvaluate Reverse Polish Notation
Operand stack evaluationFoundational
Simple mechanics, but great for testing disciplined implementation.
Common in OAs and short interviews.
ArrayMathStack
#739
MediumDaily Temperatures
Monotonic stackHighMust do
This unlocks a whole class of next-greater-element problems.
A very popular monotonic stack entry problem.
ArrayStackMonotonic Stack
#232
EasyImplement Queue using Stacks
Amortized two-stack queueHigh
Good for explaining trade-offs and amortized complexity.
Often used when interviewers want a quick design question.
StackDesignQueue
Pattern track
Back to topBinary Search
Binary search is not just one problem. The real skill is spotting monotonicity and choosing the right invariant.
#704
EasyBinary Search
Classic half-interval searchFoundationalMust do
The baseline template you should be able to write from memory.
Basic screening question.
ArrayBinary Search
#33
MediumSearch in Rotated Sorted Array
Search with sorted-half detectionHighMust do
Forces you to reason about which side is trustworthy.
Very common medium binary-search question.
ArrayBinary Search
#153
MediumFind Minimum in Rotated Sorted Array
Pivot binary searchHigh
Builds intuition for narrowing toward the unsorted edge.
Often paired with rotated-array search questions.
ArrayBinary Search
#34
MediumFind First and Last Position of Element in Sorted Array
Lower bound and upper boundHigh
Teaches boundary-search variants cleanly.
Useful OA pattern for range queries.
ArrayBinary Search
#875
MediumKoko Eating Bananas
Binary search on answerCapstoneMust do
This is the bridge from array search to optimization problems.
A canonical “search on answer” interview problem.
ArrayBinary Search
Pattern track
Back to topTrees and BST
Tree questions make up a huge chunk of interview prep. Focus on traversal templates first, then BST-specific reasoning.
#104
EasyMaximum Depth of Binary Tree
DFS height recursionFoundational
The simplest tree recurrence and a perfect warm-up.
Common first tree question.
TreeDepth-First SearchBreadth-First SearchBinary Tree
#226
EasyInvert Binary Tree
Recursive swapFoundational
Tiny problem, but it tests recursion confidence.
Frequently used as a quick tree sanity check.
TreeDepth-First SearchBreadth-First SearchBinary Tree
#100
EasySame Tree
Parallel DFS comparisonFoundational
Helpful for building structural-recursion discipline.
Common early-stage tree question.
TreeDepth-First SearchBreadth-First SearchBinary Tree
#102
MediumBinary Tree Level Order Traversal
Queue-based BFSHighMust do
This is the core level-processing template.
A frequent BFS tree question.
TreeBreadth-First SearchBinary Tree
#98
MediumValidate Binary Search Tree
Range validationHighMust do
A foundational BST correctness problem.
Popular because naive local checks fail.
TreeDepth-First SearchBinary Search TreeBinary Tree
#230
MediumKth Smallest Element in a BST
Inorder traversalHigh
A clean example of exploiting BST ordering.
Frequent BST follow-up question.
TreeDepth-First SearchBinary Search TreeBinary Tree
#199
MediumBinary Tree Right Side View
Right-first DFS or level BFSHigh
Combines traversal order with output-shaping.
Regular medium tree interview question.
TreeDepth-First SearchBreadth-First SearchBinary Tree
Pattern track
Back to topGraphs and Grid Traversal
Many placements avoid very heavy graph theory and instead focus on traversal fluency. These are the practical graph questions to master.
#733
EasyFlood Fill
Grid DFSFoundational
Simple traversal base case practice for matrix problems.
Common matrix traversal warm-up.
ArrayDepth-First SearchBreadth-First SearchMatrix
#200
MediumNumber of Islands
Connected component countingHighMust do
One of the most important graph/grid patterns in interviews.
Extremely common across interview lists.
ArrayDepth-First SearchBreadth-First SearchUnion FindMatrix
#994
MediumRotting Oranges
Multi-source BFSHighMust do
The best starting point for time-layer BFS reasoning.
Very common grid BFS problem.
ArrayBreadth-First SearchMatrix
#133
MediumClone Graph
Graph DFS with visited mapHigh
Introduces graph copying and cycle-safe traversal.
Popular medium graph question.
Hash TableDepth-First SearchBreadth-First SearchGraph
#207
MediumCourse Schedule
Cycle detection in directed graphCapstoneMust do
A topological-sort staple for interviews.
Very common in graph-heavy company lists.
Depth-First SearchBreadth-First SearchGraphTopological Sort
#417
MediumPacific Atlantic Water Flow
Reverse multi-source DFSCapstone
A strong capstone for thinking from destination to source.
Appears in strong-medium to hard interview rounds.
ArrayDepth-First SearchBreadth-First SearchMatrix
Pattern track
Back to topHeaps, Greedy, and DP
This final section is where a lot of selection happens. Strong candidates turn these from scary topics into repeatable templates.
#973
MediumK Closest Points to Origin
Heap on distanceHigh
A clean intro to top-k heap problems.
Common heap question in OAs.
ArrayMathDivide and ConquerGeometrySortingHeap
#215
MediumKth Largest Element in an Array
Min-heap of size kHigh
A core heap pattern that shows up in many data-stream problems.
Very common top-k interview question.
ArrayDivide and ConquerSortingHeapQuickselect
#435
MediumNon-overlapping Intervals
Greedy by finishing timeHigh
Great for learning why the locally optimal choice is globally safe.
A classic greedy interview problem.
ArrayDynamic ProgrammingGreedySortingIntervals
#70
EasyClimbing Stairs
1D DP recurrenceFoundational
The easiest way to internalize DP state transitions.
Standard DP warm-up.
MathDynamic ProgrammingMemoization
#198
MediumHouse Robber
Take or skip DPFoundationalMust do
A must-know recurrence for linear DP.
One of the most assigned DP questions.
ArrayDynamic Programming
#322
MediumCoin Change
Minimum coins DPHighMust do
A useful unbounded-choice DP template.
Frequent medium DP interview problem.
ArrayDynamic ProgrammingBreadth-First Search
#139
MediumWord Break
Prefix DP with dictionary lookupHigh
Blends string reasoning with DP states.
A common follow-up after string practice.
Hash TableStringDynamic ProgrammingTrieMemoization
#300
MediumLongest Increasing Subsequence
Quadratic DP baselineCapstone
Important for recognizing extend-or-restart style subsequence DP.
Well-known DP benchmark problem.
ArrayBinary SearchDynamic Programming
#1143
MediumLongest Common Subsequence
2D sequence DPCapstoneMust do
A foundational table DP that teaches matching-vs-skipping decisions.
Very common in placements and theory-heavy interviews.
StringDynamic Programming
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