Interview warm-up

Short whiteboard warmups

Under construction

Still being built. Things may change

Total results4,880 problems

Leaf Nodes in a Tree
Easy3
Tree, DFS+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Z
Easy3
Divide and conquer, Recursion+1
No attempts yet
Time limit
0.5s
Memory limit
512 MB
Judgeable
Addition Cycle
Easy3
Simulation, Math
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Minimum String Difference
Easy3
String, Sliding window+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Underprime
Easy3
Number theory, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Least Common Multiple of at Least Three Numbers
Easy3
Math, Brute force+2
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
RGB Street
Easy3
Dynamic programming, Array
No attempts yet
Time limit
0.5s
Memory limit
128 MB
Judgeable
Josephus Permutation
Easy3
Queue, Simulation+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Come Back Home
Easy3
Backtracking, DFS+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Finding the Rank
Easy3
Array, Implementation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Strange Multiplication
Easy3
Math, String+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Dice Sum
Easy3
Brute force, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Student Numbers
Easy3
String, Brute force+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Castle Guards
Easy3
Array, Greedy+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Switches On and Off
Easy3
Simulation, Array+2
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Binary Addition
Easy3
String, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Make a Palindrome
Easy3
String, Brute force+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
DFS and BFS
Easy3
DFS, BFS+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Symmetric Difference
Easy3
Hash map, Array+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
War - Land Grab
Easy3
Array, Hash map
No attempts yet
Time limit
10s
Memory limit
512 MB
Judgeable
Shortcut Key Assignment
Easy3
Simulation, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Lee-myeon and Im-hyeon
Easy3
Number theory, Implementation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Bestseller
Easy3
Hash map, Sorting+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
D-Day
Easy3
Math, Implementation
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Decimal Digit
Easy3
Simulation, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Knight Tour
Easy3
Simulation, Array+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Missed Call
Easy3
Simulation, Implementation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Hockey
Easy3
Geometry, Implementation
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Six Degrees of Kevin Bacon
Easy3
BFS, Graph+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
K-Sejun Numbers
Easy3
Math, Number theory+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Serial Numbers
Easy3
Sorting, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Repairing Pipe Leaks
Easy3
Greedy, Sorting+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Walking
Easy3
Math, Greedy
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Make It One
Easy3
Dynamic programming, Math
No attempts yet
Time limit
0.15s
Memory limit
128 MB
Judgeable
Date Cycle Calculation
Easy3
Simulation, Math+1
No attempts yet
Time limit
2s
Memory limit
4 MB
Judgeable
Guitar Concert
Easy3
Bit manipulation, Brute force+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Maximum Product
Easy3
Math, Greedy
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Largest Lucky Number
Easy3
Recursion, Brute force+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Count Numbers Made Only of 4 and 7
Easy3
Brute force, Combinatorics+2
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Transparent Mosaic
Easy3
Array, Simulation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Greeting
Easy3
Dynamic programming
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Lost Parentheses
Easy3
Greedy, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Cyclic Words
Easy3
String, Brute force+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Yongsik Goes to Camp
Easy3
Simulation, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Youngsik and Friends' Ball Toss
Easy3
Simulation, Implementation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
I Am Pokemon Master Dasom
Easy3
Hash map, Implementation+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Common Permutation
Easy3
Hash map, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Modular Exponentiation
Easy3
Math, Number theory+1
No attempts yet
Time limit
0.5s
Memory limit
128 MB
Judgeable
Lucky Ticket
Easy3
Prefix sum, Brute force+2
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
DNA Decoding
Easy3
Simulation, String+1
No attempts yet
Time limit
5s
Memory limit
16 MB
Judgeable
Number of Trailing Zeros in a Factorial
Easy3
Math, Number theory+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Hide and Seek
Easy3
BFS, Graph
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Crossword
Easy3
String, Implementation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Card Bundle Sorting
Easy3
Heap, Greedy
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Disjoint Set Operations
Easy3
Union-find
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Cipher
Easy3
String, Simulation+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Woodcut Traces
Easy3
Simulation, Matrix+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Avoiding Food Waste
Easy3
BFS, DFS+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Prime Palindrome
Easy3
Math, Brute force+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Number Word Sort
Easy3
Sorting, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Password Generation
Easy3
Backtracking, Brute force+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Common Names
Easy3
Hash map, Sorting+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Multiple of Three
Easy3
String, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Firework Show
Easy3
Array, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Sum of Distinct Numbers
Easy3
Math, Binary search+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Logic Professor
Easy3
Brute force, Math
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Encryption Key
Easy3
Number theory, Math+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Set Difference
Easy3
Hash map, Sorting+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Cipher
Easy3
Simulation, Matrix+2
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Broken Odometer
Easy3
Math, Implementation+1
No attempts yet
Time limit
0.5s
Memory limit
128 MB
Judgeable
Median Filter
Easy3
Matrix, Sorting+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
01 Tiles
Easy3
Dynamic programming, Math
No attempts yet
Time limit
0.75s
Memory limit
256 MB
Judgeable
Carbon Compounds
Easy3
Brute force, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Maximum Subarray Sum
Easy3
Dynamic programming, Array
No attempts yet
Time limit
1s
Memory limit
128 MB
Judgeable
Tower of Hanoi
Easy3
Recursion, Math+1
No attempts yet
Time limit
6s
Memory limit
128 MB
Judgeable
Finding Numbers
Easy3
Binary search, Sorting+1
No attempts yet
Time limit
1s
Memory limit
128 MB
Judgeable
Triangle
Easy3
Geometry, Implementation+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Painted Areas
Easy3
BFS, DFS+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Minimum Heap
Easy3
Heap, Implementation
No attempts yet
Time limit
1s
Memory limit
128 MB
Judgeable
Find Prime Numbers
Easy3
Math, Number theory+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable
Meeting Room Scheduling
Easy3
Greedy, Sorting+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Integer Triangle
Easy3
Dynamic programming, Matrix
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Postfix Expression Evaluation 2
Easy3
Stack, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Jumong's Armor Materials
Easy3
Two pointers, Array+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Snail 2
Easy3
Simulation, Matrix+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Printer Queue
Easy3
Queue, Simulation
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
DNA
Easy3
String, Greedy+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Surprising String
Easy3
String, Brute force+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Travel Plan
Easy3
Union-find, Graph+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Tree Traversal
Easy3
Tree, DFS+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Overtaking
Easy3
Dynamic programming, Array+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Sum of Numbers 2
Easy3
Two pointers, Prefix sum+1
No attempts yet
Time limit
0.5s
Memory limit
128 MB
Judgeable
Counting Consecutive Sums
Easy3
Math, Number theory
No attempts yet
Time limit
2s
Memory limit
32 MB
Judgeable
Text Message
Easy3
Simulation, String+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Completing a Magic Square
Easy3
Math, Matrix+1
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
IP Network Address
Easy3
Bit manipulation, Implementation
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Negative Binary
Easy3
Math, Implementation
No attempts yet
Time limit
2s
Memory limit
128 MB
Judgeable
Downward Game
Easy3
Dynamic programming, Matrix
No attempts yet
Time limit
1s
Memory limit
4 MB
Judgeable
Pebbles
Easy3
Math, Implementation
No attempts yet
Time limit
1s
Memory limit
128 MB
Judgeable
Statistics
Easy3
Array, Sorting+1
No attempts yet
Time limit
2s
Memory limit
256 MB
Judgeable

Title	Level	Topics	Solved	Time limit	Memory limit	Judge
Leaf Nodes in a TreeGiven a tree by parent array, delete a node and all its descendants, then count how many leaf nodes remain.	Easy3	TreeDFS+1	No attempts yet	2s	128 MB	Judgeable
ZGiven N and coordinates (r,c) in a 2^N x 2^N grid, compute the visit order index of that cell under recursive Z-order (Morton order) traversal.	Easy3	Divide and conquerRecursion+1	No attempts yet	0.5s	512 MB	Judgeable
Addition CycleSimulate a digit-transformation cycle on a two-digit number until it returns to the original value and count the steps.	Easy3	SimulationMath	No attempts yet	2s	128 MB	Judgeable
Minimum String DifferenceSlide the shorter string A across every possible alignment position over B and output the minimum number of mismatched characters.	Easy3	StringSliding window+1	No attempts yet	2s	128 MB	Judgeable
UnderprimeCount integers in a range whose total number of prime factors (with multiplicity) is itself a prime number.	Easy3	Number theoryMath+1	No attempts yet	2s	128 MB	Judgeable
Least Common Multiple of at Least Three NumbersGiven five distinct positive integers up to 100, find the smallest number divisible by at least three of them, essentially the minimum LCM over all triples.	Easy3	MathBrute force+2	No attempts yet	2s	128 MB	Judgeable
RGB StreetGiven per-house costs for three colors, compute the minimum total cost to paint all houses in a line so that no two adjacent houses share a color.	Easy3	Dynamic programmingArray	No attempts yet	0.5s	128 MB	Judgeable
Josephus PermutationSimulate the Josephus elimination order for N people counting off every K-th person in a circle and print the removal sequence.	Easy3	QueueSimulation+1	No attempts yet	2s	256 MB	Judgeable
Come Back HomeCount simple paths of exact length K from the bottom-left to the top-right cell of a small grid, avoiding blocked cells and revisits.	Easy3	BacktrackingDFS+1	No attempts yet	2s	128 MB	Judgeable
Finding the RankGiven a sorted list of scores with a capacity limit, compute the rank of a new score or return -1 if the list is full and the score is not higher than the last entry.	Easy3	ArrayImplementation+1	No attempts yet	2s	128 MB	Judgeable
Strange MultiplicationGiven two large numbers as digit strings, compute the sum of all pairwise products of their digits, which equals the product of their digit sums.	Easy3	MathString+1	No attempts yet	2s	256 MB	Judgeable
Dice SumGiven three dice with sizes S1, S2, S3, find the sum value that occurs most often among all possible triples, choosing the smallest if tied.	Easy3	Brute forceMath+1	No attempts yet	2s	128 MB	Judgeable
Student NumbersGiven N equal-length numeric strings, find the smallest suffix length k so that all suffixes of length k remain distinct.	Easy3	StringBrute force+1	No attempts yet	2s	128 MB	Judgeable
Castle GuardsGiven a grid of guards, compute the minimum number of guards to add so every row and column has at least one, which equals the max of empty-row count and empty-column count.	Easy3	ArrayGreedy+1	No attempts yet	2s	128 MB	Judgeable
Switches On and OffSimulate switch toggles where male students flip every multiple of their number and female students flip the largest symmetric interval centered on their number.	Easy3	SimulationArray+2	No attempts yet	2s	128 MB	Judgeable
Binary AdditionAdd two binary strings up to 80 digits long and print the sum in binary without leading zeros.	Easy3	StringMath+1	No attempts yet	2s	128 MB	Judgeable
Make a PalindromeGiven a lowercase string of length at most 50, find the minimum length of a palindrome obtained by appending characters only to its end.	Easy3	StringBrute force+1	No attempts yet	2s	128 MB	Judgeable
DFS and BFSGiven an undirected graph, output the vertex visit order for DFS then BFS starting from a given vertex, always preferring the smallest-numbered neighbor.	Easy3	DFSBFS+1	No attempts yet	2s	128 MB	Judgeable
Symmetric DifferenceGiven two sets of natural numbers, compute the size of their symmetric difference.	Easy3	Hash mapArray+1	No attempts yet	2s	256 MB	Judgeable
War - Land GrabFor each region's list of soldier army IDs, find the majority element that appears more than half the time, or print SYJKGW if none exists.	Easy3	ArrayHash map	No attempts yet	10s	512 MB	Judgeable
Shortcut Key AssignmentAssign each menu option an unused shortcut letter by checking word-initial letters first, then any letter in the string, following the options in order.	Easy3	SimulationString+1	No attempts yet	2s	128 MB	Judgeable
Lee-myeon and Im-hyeonClassify a number 1 to 2700 as Lee-myeon and/or Im-hyeon based on digit sum parity and prime factorization rules, then output one of four codes.	Easy3	Number theoryImplementation+1	No attempts yet	2s	128 MB	Judgeable
BestsellerGiven N book titles sold in a day, find the most frequent title, breaking ties by lexicographically smallest.	Easy3	Hash mapSorting+1	No attempts yet	2s	128 MB	Judgeable
D-DayCompute the number of days between two calendar dates accounting for leap years, printing 'gg' if the gap reaches 1000 years or more.	Easy3	MathImplementation	No attempts yet	2s	128 MB	Judgeable
Decimal DigitSimulate long division of A by B to output the N-th digit after the decimal point.	Easy3	SimulationMath+1	No attempts yet	2s	128 MB	Judgeable
Knight TourCheck whether a given sequence of 36 squares on a 6x6 board forms a valid closed knight's tour with legal moves between consecutive squares and back to the start.	Easy3	SimulationArray+1	No attempts yet	2s	128 MB	Judgeable
Missed CallSimulate an album of N songs with 5-second gaps and a phone ringing every D seconds to find the first ring Kangto can actually hear.	Easy3	SimulationImplementation+1	No attempts yet	2s	128 MB	Judgeable
HockeyCount how many given points lie inside or on the boundary of a stadium shape formed by a rectangle and two semicircular ends.	Easy3	GeometryImplementation	No attempts yet	2s	128 MB	Judgeable
Six Degrees of Kevin BaconGiven an unweighted friendship graph, find the vertex whose sum of shortest distances to all others is minimal, breaking ties by smallest index.	Easy3	BFSGraph+1	No attempts yet	2s	128 MB	Judgeable
K-Sejun NumbersCount integers from 1 to N whose every prime factor is at most K, given N up to 100000 and K up to 100.	Easy3	MathNumber theory+1	No attempts yet	2s	128 MB	Judgeable
Serial NumbersSort serial numbers by length, then digit-sum, then a custom lexicographic rule where digits precede letters.	Easy3	SortingString+1	No attempts yet	2s	128 MB	Judgeable
Repairing Pipe LeaksGiven leak positions and a fixed tape length, compute the minimum number of length-L tapes needed so each leak is covered with at least 0.5 margin on both sides.	Easy3	GreedySorting+1	No attempts yet	2s	128 MB	Judgeable
WalkingCompute the minimum time to walk from (0,0) to (X,Y) on a grid where straight moves cost W and diagonal moves cost S.	Easy3	MathGreedy	No attempts yet	2s	128 MB	Judgeable
Make It OneCompute the minimum number of divide-by-3, divide-by-2, or subtract-1 operations needed to reduce N to 1.	Easy3	Dynamic programmingMath	No attempts yet	0.15s	128 MB	Judgeable
Date Cycle CalculationFind the smallest year whose Earth, Sun, and Moon cycle counters, each resetting at fixed limits, match a given triple of values.	Easy3	SimulationMath+1	No attempts yet	2s	4 MB	Judgeable
Guitar ConcertGiven up to 10 guitars each covering a subset of up to 50 songs, find the minimum number of guitars needed to play the maximum possible number of songs.	Easy3	Bit manipulationBrute force+1	No attempts yet	2s	128 MB	Judgeable
Maximum ProductSplit S into K positive integers as equal as possible to maximize their product, given S and K up to 100 and 20.	Easy3	MathGreedy	No attempts yet	2s	128 MB	Judgeable
Largest Lucky NumberGiven N up to 1,000,000, find the largest number no greater than N whose digits are only 4s and 7s.	Easy3	RecursionBrute force+1	No attempts yet	2s	256 MB	Judgeable
Count Numbers Made Only of 4 and 7Count integers between A and B (up to 1e9) whose digits are all 4s and 7s.	Easy3	Brute forceCombinatorics+2	No attempts yet	2s	128 MB	Judgeable
Transparent MosaicGiven N rectangular paper sheets on a 100x100 grid, count cells covered by more than M sheets.	Easy3	ArraySimulation+1	No attempts yet	2s	128 MB	Judgeable
GreetingGiven health costs and joy values for up to 20 people, pick a subset maximizing total joy while keeping total health loss below 100.	Easy3	Dynamic programming	No attempts yet	2s	128 MB	Judgeable
Lost ParenthesesGiven an arithmetic expression with only plus and minus signs, place parentheses to minimize the evaluated result.	Easy3	GreedyString+1	No attempts yet	2s	128 MB	Judgeable
Cyclic WordsCount how many words are distinct once each is allowed to be read starting from any position around a circle.	Easy3	StringBrute force+1	No attempts yet	2s	128 MB	Judgeable
Yongsik Goes to CampFor N bus schedules given by first departure, interval, and count, find the minimum wait until Yongsik can board any bus after arriving at time T, or -1 if none is available.	Easy3	SimulationMath+1	No attempts yet	2s	128 MB	Judgeable
Youngsik and Friends' Ball TossSimulate a ball being passed clockwise or counterclockwise by L seats depending on parity of catch count, counting throws until someone catches it M times.	Easy3	SimulationImplementation+1	No attempts yet	2s	128 MB	Judgeable
I Am Pokemon Master DasomBuild a bidirectional mapping between Pokemon numbers and names, then answer up to 100,000 lookup queries either way.	Easy3	Hash mapImplementation+1	No attempts yet	2s	256 MB	Judgeable
Common PermutationFor each pair of input strings, count letter frequencies and output the multiset intersection sorted alphabetically as the longest common rearranged subsequence.	Easy3	Hash mapString+1	No attempts yet	2s	128 MB	Judgeable
Modular ExponentiationCompute A raised to the power B modulo C efficiently using fast modular exponentiation.	Easy3	MathNumber theory+1	No attempts yet	0.5s	128 MB	Judgeable
Lucky TicketFind the longest even-length substring of a digit string whose first half digit sum equals its second half digit sum.	Easy3	Prefix sumBrute force+2	No attempts yet	2s	128 MB	Judgeable
DNA DecodingRepeatedly merge the last two bases of a DNA string using a fixed lookup table until one base remains, then output it.	Easy3	SimulationString+1	No attempts yet	5s	16 MB	Judgeable
Number of Trailing Zeros in a FactorialCount the trailing zeros of N! for N up to 500 by counting factors of 5.	Easy3	MathNumber theory+1	No attempts yet	2s	128 MB	Judgeable
Hide and SeekCompute the minimum number of moves to reach position K from N on the number line using BFS with steps +1, -1, or doubling.	Easy3	BFSGraph	No attempts yet	2s	128 MB	Judgeable
CrosswordGiven a filled crossword grid, extract every maximal horizontal or vertical run of letters of length at least two and output the lexicographically smallest such word.	Easy3	StringImplementation+1	No attempts yet	2s	128 MB	Judgeable
Card Bundle SortingGiven N sorted card bundle sizes, find the minimum total comparisons to merge them all into one bundle using an optimal merge strategy (classic huffman-like heap problem).	Easy3	HeapGreedy	No attempts yet	2s	128 MB	Judgeable
Disjoint Set OperationsImplement a union-find structure that merges sets and answers whether two elements share a set across a sequence of operations.	Easy3	Union-find	No attempts yet	2s	128 MB	Judgeable
CipherEncrypt a lowercase text by shifting each letter backward in the alphabet by the position value of a repeating key letter, leaving spaces unchanged but still consuming a key character.	Easy3	StringSimulation+1	No attempts yet	2s	256 MB	Judgeable
Woodcut TracesSimulate a tool moving on an N by N grid following U/D/L/R commands, ignoring out-of-bounds moves, and mark each point as unvisited, vertical-only, horizontal-only, or both.	Easy3	SimulationMatrix+1	No attempts yet	2s	128 MB	Judgeable
Avoiding Food WasteGiven a grid marked with food waste cells, find the size of the largest 4-directionally connected component using BFS/DFS or union-find.	Easy3	BFSDFS+1	No attempts yet	2s	128 MB	Judgeable
Prime PalindromeFind the smallest number greater than or equal to N that is both a prime and a palindrome.	Easy3	MathBrute force+1	No attempts yet	2s	256 MB	Judgeable
Number Word SortSort integers from M to N by comparing their digits spelled out as English words rather than by numeric value, then print 10 per line.	Easy3	SortingString+1	No attempts yet	2s	128 MB	Judgeable
Password GenerationGenerate all length-L increasing letter combinations from a given set of C letters that contain at least one vowel and two consonants, printed in lexicographic order.	Easy3	BacktrackingBrute force+1	No attempts yet	2s	128 MB	Judgeable
Common NamesGiven two lists of unique lowercase names, find and print the count and sorted list of names common to both.	Easy3	Hash mapSorting+1	No attempts yet	2s	256 MB	Judgeable
Multiple of ThreeGiven a huge number as a digit string, repeatedly sum its digits until one digit remains, then report how many steps it took and whether the number is divisible by 3.	Easy3	StringMath+1	No attempts yet	2s	128 MB	Judgeable
Firework ShowGiven N firework periods and an end time C, count how many distinct seconds from 1 to C have at least one firework fired by any student.	Easy3	ArrayMath+1	No attempts yet	2s	128 MB	Judgeable
Sum of Distinct NumbersGiven a sum S, find the largest number of distinct positive integers that can add up to exactly S.	Easy3	MathBinary search+1	No attempts yet	2s	128 MB	Judgeable
Logic ProfessorGiven N statements each claiming exactly x of them are true, find the largest consistent count of true statements or -1 if none works.	Easy3	Brute forceMath	No attempts yet	2s	128 MB	Judgeable
Encryption KeyDetermine for each large number S whether all its prime factors exceed one million, using trial division up to that bound.	Easy3	Number theoryMath+1	No attempts yet	2s	128 MB	Judgeable
Set DifferenceGiven two sets of up to 500,000 natural numbers each, output the count and sorted list of elements present in A but not in B.	Easy3	Hash mapSorting+1	No attempts yet	2s	256 MB	Judgeable
CipherGiven an encrypted string built by zigzag row reading of a column-filled table, reconstruct the original string for a given number of columns.	Easy3	SimulationMatrix+2	No attempts yet	2s	128 MB	Judgeable
Broken OdometerConvert an odometer reading that skips the digit 4 back into the real distance traveled, using a base-9-like digit mapping.	Easy3	MathImplementation+1	No attempts yet	0.5s	128 MB	Judgeable
Median FilterApply a 3x3 median filter over an image and count filtered pixels whose median value is at least a given threshold.	Easy3	MatrixSorting+1	No attempts yet	2s	128 MB	Judgeable
01 TilesCount length-N binary strings tileable by '1' and '00' pieces, modulo 15746, which reduces to a Fibonacci recurrence.	Easy3	Dynamic programmingMath	No attempts yet	0.75s	256 MB	Judgeable
Carbon CompoundsParse three molecules of C,H,O atoms and find coefficients 1 to 10 for each side that balance atom counts, lexicographically smallest.	Easy3	Brute forceString+1	No attempts yet	2s	128 MB	Judgeable
Maximum Subarray SumGiven up to 100,000 integers, compute the maximum sum of a non-empty contiguous subarray.	Easy3	Dynamic programmingArray	No attempts yet	1s	128 MB	Judgeable
Tower of HanoiPrint the minimum move count for Tower of Hanoi with N disks, using big-integer count for N up to 100 and the explicit move sequence when N is at most 20.	Easy3	RecursionMath+1	No attempts yet	6s	128 MB	Judgeable
Finding NumbersGiven N integers and M queries, output for each query whether it exists in the array, requiring an efficient lookup method.	Easy3	Binary searchSorting+1	No attempts yet	1s	128 MB	Judgeable
TriangleGiven three points, classify the triangle they form as degenerate, equilateral, isosceles or scalene, and further by its largest angle type.	Easy3	GeometryImplementation+1	No attempts yet	2s	128 MB	Judgeable
Painted AreasCount connected components of 1-cells in a grid (4-directional adjacency) and output the count and the size of the largest component.	Easy3	BFSDFS+1	No attempts yet	2s	128 MB	Judgeable
Minimum HeapImplement a min-heap to support inserting natural numbers and repeatedly extracting the smallest, printing 0 when empty.	Easy3	HeapImplementation	No attempts yet	1s	128 MB	Judgeable
Find Prime NumbersPrint all prime numbers between two given bounds M and N, one per line, using an efficient sieve up to 1,000,000.	Easy3	MathNumber theory+1	No attempts yet	2s	256 MB	Judgeable
Meeting Room SchedulingGiven N meetings with start and end times, select the maximum number of non-overlapping meetings using a classic greedy interval scheduling approach.	Easy3	GreedySorting+1	No attempts yet	2s	128 MB	Judgeable
Integer TriangleGiven a triangle of up to 500 rows, compute the maximum sum path from top to bottom moving diagonally at each step.	Easy3	Dynamic programmingMatrix	No attempts yet	2s	128 MB	Judgeable
Postfix Expression Evaluation 2Evaluate a postfix expression using given operand values and print the result rounded to two decimal places.	Easy3	StackString+1	No attempts yet	2s	128 MB	Judgeable
Jumong's Armor MaterialsCount how many pairs of given numbers sum to a target value M, using each material at most once per pair.	Easy3	Two pointersArray+1	No attempts yet	2s	128 MB	Judgeable
Snail 2Simulate a snail-like spiral fill on an M by N grid and count how many times the path turns before every cell is visited.	Easy3	SimulationMatrix+1	No attempts yet	2s	128 MB	Judgeable
Printer QueueSimulate a queue where documents are printed only when no higher-priority document remains, and find the print order of a specific document.	Easy3	QueueSimulation	No attempts yet	2s	128 MB	Judgeable
DNAGiven N DNA strings of length M, construct the string minimizing total Hamming distance to all, breaking ties lexicographically, and output that distance.	Easy3	StringGreedy+1	No attempts yet	2s	128 MB	Judgeable
Surprising StringFor each string, check for every gap size whether all pairs of letters at that fixed distance are distinct, and report if the string is 'surprising'.	Easy3	StringBrute force+1	No attempts yet	2s	128 MB	Judgeable
Travel PlanGiven an adjacency matrix of cities, decide if consecutive cities in a given visit order all lie in the same connected component.	Easy3	Union-findGraph+1	No attempts yet	2s	128 MB	Judgeable
Tree TraversalBuild a binary tree from parent-child input and print its preorder, inorder, and postorder traversals.	Easy3	TreeDFS+1	No attempts yet	2s	128 MB	Judgeable
OvertakingGiven entry and exit orders of N cars, count how many cars are not part of the longest common subsequence, meaning they overtook someone.	Easy3	Dynamic programmingArray+1	No attempts yet	2s	128 MB	Judgeable
Sum of Numbers 2Given N positive integers and a target M, count contiguous subarrays whose sum equals M.	Easy3	Two pointersPrefix sum+1	No attempts yet	0.5s	128 MB	Judgeable
Counting Consecutive SumsCount the number of ways to express a given natural number N as a sum of one or more consecutive natural numbers.	Easy3	MathNumber theory	No attempts yet	2s	32 MB	Judgeable
Text MessageSimulate typing a message on a numeric keypad, summing key press costs and extra wait times when consecutive characters share a key (except spaces).	Easy3	SimulationString+1	No attempts yet	2s	128 MB	Judgeable
Completing a Magic SquareGiven a 3x3 magic square with up to three cells erased (marked 0), fill in the missing positive integers so all rows, columns, and diagonals share the same sum.	Easy3	MathMatrix+1	No attempts yet	2s	128 MB	Judgeable
IP Network AddressGiven a list of IPv4 addresses, compute the smallest common network address and its mask that covers them all using bitwise operations.	Easy3	Bit manipulationImplementation	No attempts yet	2s	128 MB	Judgeable
Negative BinaryConvert a given decimal integer into its base -2 (negabinary) representation.	Easy3	MathImplementation	No attempts yet	2s	128 MB	Judgeable
Downward GameGiven an N x 3 grid with limited column transitions between rows, compute the maximum and minimum total path sums from top to bottom.	Easy3	Dynamic programmingMatrix	No attempts yet	1s	4 MB	Judgeable
PebblesGiven N pebbles to place on grid points, compute the minimum possible perimeter of the smallest bounding rectangle covering all of them.	Easy3	MathImplementation	No attempts yet	1s	128 MB	Judgeable
StatisticsGiven N odd integers, compute and print the rounded mean, median, mode (second smallest if tied), and range.	Easy3	ArraySorting+1	No attempts yet	2s	256 MB	Judgeable