Interview hard

Hard final-round questions

Under construction

Still being built. Things may change

Total results64 problems

Paper RouteHard8
Graph, DFS +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
A Brief GerrymanderHard8
Dynamic programming, Sorting +1No attempts yetTime limit1sMemory limit128 MB
Judgeable
Spare the Ewoks!Hard8
Dynamic programming, Prefix sum +1No attempts yetTime limit3sMemory limit128 MB
Judgeable
Repair DepotsHard8
Binary search, Geometry +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
Core WarsHard8
Simulation, Implementation +1No attempts yetTime limit1sMemory limit128 MB
Judgeable
Quick SearchHard8
Graph, Dynamic programming +1No attempts yetTime limit1sMemory limit128 MB
Judgeable
The DoorsHard8
Geometry, Graph +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
Game of StonesHard8
Game theory, Graph +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
Escaping the Tutoring HouseHard8
Geometry, Graph +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
ClockHard8
Geometry, Divide and conquer +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
The Pharaoh's CurseHard8
BFS, Graph +2No attempts yetTime limit5sMemory limit128 MB
Judgeable
Fat NinjasHard8
Geometry, Union-find +2No attempts yetTime limit3sMemory limit128 MB
Judgeable
StarCowraftHard8
Geometry, Math +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
Doing WindowsHard8
Geometry, Math +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
CensorshipHard8
Dynamic programming, String +1No attempts yetTime limit1sMemory limit128 MB
Judgeable
One-Way RoadsHard8
Graph, DFS +2No attempts yetTime limit2sMemory limit64 MB
Judgeable
Prison rearrangementHard8
Graph, BFS +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
IslandHard8
Tree, DFS +2No attempts yetTime limit1sMemory limit128 MB
Judgeable
SchoolsHard8
Greedy, Dynamic programming +2No attempts yetTime limit3sMemory limit128 MB
Judgeable
PlotHard8
Binary search, Dynamic programming +2No attempts yetTime limit30sMemory limit128 MB
Judgeable
Finding an integerHard8
Greedy, Implementation +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Laser TowersHard8
Greedy, Brute force +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Substitution Cipher KeyHard8
Greedy, Sorting +2No attempts yetTime limit1sMemory limit64 MB
Judgeable
Feasible roundingHard8
Greedy, Matrix +2No attempts yetTime limit1sMemory limit512 MB
Judgeable
Tire PatchesHard8
Dynamic programming, Array +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
War Among the StarsHard8
Geometry, Implementation +1No attempts yetTime limit2sMemory limit512 MB
Judgeable
Palindrome cipher decryptionHard8
Dynamic programming, String +2No attempts yetTime limit8sMemory limit512 MB
Judgeable
Splitting Game LevelsHard8
Dynamic programming, Divide and conquer +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Wolves 2Hard8
Dynamic programming, Prefix sum +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
I Teach SweepingHard8
Geometry, Sorting +1No attempts yetTime limit2sMemory limit512 MB
Judgeable
Company Culture 4Hard8
Tree, Prefix sum +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Imbalance ObviationHard8
Greedy, Implementation +2No attempts yetTime limit20sMemory limit1024 MB
Judgeable
Monday BluesHard8
Graph, Minimum spanning tree +2No attempts yetTime limit1sMemory limit512 MB
Judgeable
Alien microbesHard8
Dynamic programming, Combinatorics +2No attempts yetTime limit2sMemory limit256 MB
Judgeable
Shooting GalleryHard8
Dynamic programming, Array +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
SumdokuHard8
Backtracking, Implementation +1No attempts yetTime limit2sMemory limit512 MB
Judgeable
Ladder ManipulationHard8
Backtracking, Brute force +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Snow BootsHard8
Binary search, Sorting +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
XEN 3166Hard8
Greedy, String +1No attempts yetTime limit2sMemory limit512 MB
Judgeable
CitationsHard8
Tree, Greedy +2No attempts yetTime limit1sMemory limit1024 MB
Judgeable
Word ClockHard8
Backtracking, Implementation +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Amateur Radio NetworkHard8
Geometry, Binary search +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Grumpy Groundhogs in GridlandHard8
Graph, BFS +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Hiding MerlinHard8
String matching, Dynamic programming +2No attempts yetTime limit4sMemory limit512 MB
Judgeable
I'm a FanHard8
Geometry, Math +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
ParcelHard8
Two pointers, Hash map +1No attempts yetTime limit1sMemory limit512 MB
Judgeable
Harry the HamsterHard8
Game theory, Dynamic programming +2No attempts yetTime limit3sMemory limit512 MB
Judgeable
Count the BitsHard8
Dynamic programming, Bit manipulation +1No attempts yetTime limit2sMemory limit512 MB
Judgeable
Maple Leaf StoryHard8
Brute force, Combinatorics +2No attempts yetTime limit1sMemory limit256 MB
Judgeable
cmpHard8
Bit manipulation, Binary search +2No attempts yetTime limit10sMemory limit256 MB
Judgeable
Bad KemingHard8
String matching, String +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Expression TreeHard8
Tree, Greedy +2No attempts yetTime limit1sMemory limit256 MB
Judgeable
Shopping MallHard8
Simulation, Heap +2No attempts yetTime limit1sMemory limit512 MB
Judgeable
NM and K (1)Hard8
Dynamic programming, Bit manipulation +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Right-hand obstructionHard8
Simulation, Queue +2No attempts yetTime limit1sMemory limit512 MB
Judgeable
QuadtreeHard8
Tree, Dynamic programming +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Universal and Existential QuantifiersHard8
Greedy, Sorting +2No attempts yetTime limit2sMemory limit512 MB
Judgeable
Computational IchthyologyHard8
Greedy, Simulation +2No attempts yetTime limit2sMemory limit1024 MB
Judgeable
NamesHard8
String, Greedy +1No attempts yetTime limit2sMemory limit1024 MB
Judgeable
String RemovalHard8
Dynamic programming, String matching +2No attempts yetTime limit1sMemory limit512 MB
Judgeable
ConsulHard8
Divide and conquer, Brute force +2No attempts yetTime limit1sMemory limit512 MB
Judgeable
Longest Increasing SequenceHard8
Dynamic programming, Prefix sum +2No attempts yetTime limit5sMemory limit512 MB
Judgeable
TerrorHard8
Backtracking, Recursion +2No attempts yetTime limit2.5sMemory limit1024 MB
Judgeable
GCD and Shortest PathHard8
Number theory, Graph +2No attempts yetTime limit1sMemory limit1024 MB
Judgeable

Title	Level	Topics	Solved	Time limit	Memory limit	Judge
Paper RouteWith N+1 nodes and exactly N roads, find the cheapest closed walk from node 0 covering all addresses, then add the campus travel cost from wherever you end.	Hard8	GraphDFS+2	No attempts yet	1s	128 MB	Judgeable
A Brief GerrymanderChoose A avenue boundaries including 1 and 100 to maximize the number of vertical strips that contain at least one marked neighborhood, given fixed street boundaries.	Hard8	Dynamic programmingSorting+1	No attempts yet	1s	128 MB	Judgeable
Spare the Ewoks!Given an m by n grid with blocked cells, choose up to three non-overlapping axis-aligned rectangles to maximize the total covered area.	Hard8	Dynamic programmingPrefix sum+1	No attempts yet	3s	128 MB	Judgeable
Repair DepotsPlace at most c depots anywhere in the plane to minimize the largest distance from any of n bots (n at most 16) to its nearest depot, and print that distance to six decimals.	Hard8	Binary searchGeometry+2	No attempts yet	1s	128 MB	Judgeable
Core WarsSimulate 8000-cell Redcode MARS with three addressing modes and report which warrior survives or if they tie after 32000 steps.	Hard8	SimulationImplementation+1	No attempts yet	1s	128 MB	Judgeable
Quick SearchGiven a small graph and k officers all starting at A, find the minimum time for the officers to jointly visit every node, where each officer walks a path.	Hard8	GraphDynamic programming+1	No attempts yet	1s	128 MB	Judgeable
The DoorsGiven up to 18 vertical walls, each with two doorways, find the shortest path from (0,5) to (10,5) inside a 10x10 square without crossing any solid segment.	Hard8	GeometryGraph+2	No attempts yet	1s	128 MB	Judgeable
Game of StonesGiven a directed acyclic graph with stones on nodes, two players alternately slide one stone along an edge; decide whether the first player wins.	Hard8	Game theoryGraph+2	No attempts yet	1s	128 MB	Judgeable
Escaping the Tutoring HouseFind whether a tutor can reach the exit while keeping all kids inside a forward half-plane at every instant, and if so, the shortest such path.	Hard8	GeometryGraph+2	No attempts yet	1s	128 MB	Judgeable
ClockFind the largest empty circle fully inside a rectangular wall that avoids up to 50 non-overlapping discs, using a generalized Voronoi diagram of points, segments, and circles.	Hard8	GeometryDivide and conquer+2	No attempts yet	1s	128 MB	Judgeable
The Pharaoh's CurseOn a small grid, S pushes up to two sarcophagi onto buttons while stepping around them, and must reach the exit with all buttons held; find the minimum steps or report impossible.	Hard8	BFSGraph+2	No attempts yet	5s	128 MB	Judgeable
Fat NinjasGiven point sensors in an N by N square, find the diameter of the largest circle that can travel from the left side to the right side without touching any sensor.	Hard8	GeometryUnion-find+2	No attempts yet	3s	128 MB	Judgeable
StarCowraftGiven test battle outcomes and the constraint that no unit strength exceeds 100 times another, determine for each new battle whether one army must win or the result is undecidable.	Hard8	GeometryMath+2	No attempts yet	1s	128 MB	Judgeable
Doing WindowsGiven a screen and four windows with fixed aspect ratios, decide whether the windows can be resized and placed to tile the screen with no gaps or overlaps.	Hard8	GeometryMath+2	No attempts yet	1s	128 MB	Judgeable
CensorshipGiven a text and a filter word set, remove occurrences repeatedly to make the shortest possible result and report its length.	Hard8	Dynamic programmingString+1	No attempts yet	1s	128 MB	Judgeable
One-Way RoadsDecide whether the undirected streets of a graph can all be oriented so that each required ordered pair stays reachable from the first to the second.	Hard8	GraphDFS+2	No attempts yet	2s	64 MB	Judgeable
Prison rearrangementGiven a bipartite conflict graph between two prisons of size m, find the largest k <= m/2 so that k prisoners can be swapped across while keeping every conflicting pair apart.	Hard8	GraphBFS+2	No attempts yet	1s	128 MB	Judgeable
IslandGiven all pairwise shortest tolls among the n seaside triangles, recover the adjacency structure and edge weights of the underlying border tree.	Hard8	TreeDFS+2	No attempts yet	1s	128 MB	Judgeable
SchoolsAssign a distinct number 1..n to each school within its allowed interval, minimizing the total weighted movement cost.	Hard8	GreedyDynamic programming+2	No attempts yet	3s	128 MB	Judgeable
PlotPartition a sequence of n points into at most m contiguous groups, replacing each group with one point, to minimize the maximum distance from any original point to its group's representative.	Hard8	Binary searchDynamic programming+2	No attempts yet	30s	128 MB	Judgeable
Finding an integerFind the smallest integer at least N whose decimal digits contain d1 at least c1 times and d2 at least c2 times.	Hard8	GreedyImplementation+2	No attempts yet	2s	512 MB	Judgeable
Laser TowersOn a grid with directional laser towers and enemy counts, choose which towers fire and at which cell so lasers never intersect, maximizing enemies destroyed.	Hard8	GreedyBrute force+2	No attempts yet	2s	512 MB	Judgeable
Substitution Cipher KeyGiven N distinct words and a target permutation, find the lexicographically smallest substitution cipher key that sorts the encrypted words into that order, or report none.	Hard8	GreedySorting+2	No attempts yet	1s	64 MB	Judgeable
Feasible roundingRound each decimal entry to floor or ceiling so that every row and column sum still matches its stated total, choosing the lexicographically smallest whole table.	Hard8	GreedyMatrix+2	No attempts yet	1s	512 MB	Judgeable
Tire PatchesOn a circular tire, cover all hole positions with the minimum total length of uncut patches of two given lengths and return that total length.	Hard8	Dynamic programmingArray+2	No attempts yet	2s	512 MB	Judgeable
War Among the StarsCompute the shortest distance between two tetrahedra in space, given the coordinates of their eight vertices.	Hard8	GeometryImplementation+1	No attempts yet	2s	512 MB	Judgeable
Palindrome cipher decryptionFor each string, find its longest palindromic subsequence and output the lexicographically smallest one among those of maximal length.	Hard8	Dynamic programmingString+2	No attempts yet	8s	512 MB	Judgeable
Splitting Game LevelsPartition n levels into k consecutive groups to minimize the expected total time of a random coin-draw process, and print it to six decimals.	Hard8	Dynamic programmingDivide and conquer+2	No attempts yet	2s	512 MB	Judgeable
Wolves 2Count binary strings of length N in which every given interval contains at most two ones, modulo 1e9+7.	Hard8	Dynamic programmingPrefix sum+2	No attempts yet	2s	512 MB	Judgeable
I Teach SweepingGiven segments in the first quadrant, find a line through the origin that intersects the most segments and report that count.	Hard8	GeometrySorting+1	No attempts yet	2s	512 MB	Judgeable
Company Culture 4On a rooted tree, praise spreads downward from an employee to all descendants or upward to all ancestors, the direction flips over time, and queries ask for an employee's accumulated praise.	Hard8	TreePrefix sum+2	No attempts yet	2s	512 MB	Judgeable
Imbalance ObviationAssign each marble L or R so the pan difference stays within 1 during insertion in order and during a given removal permutation; output the lexicographically smallest assignment.	Hard8	GreedyImplementation+2	No attempts yet	20s	1024 MB	Judgeable
Monday BluesGiven an N by M grid with costly buildable cells and blocked or unbuildable cells, find the minimum total cost to cut every path from (1,1) to (N,M), or report that no placement can do it.	Hard8	GraphMinimum spanning tree+2	No attempts yet	1s	512 MB	Judgeable
Alien microbesCount the breeding patterns over H days starting from one microbe, where each day the microbes alive produce children with a total of at most W.	Hard8	Dynamic programmingCombinatorics+2	No attempts yet	2s	256 MB	Judgeable
Shooting GalleryA row of ducks, each with a species; a good round hits two ducks of the same species and keeps only the ducks strictly between them, and rounds continue while same-species pairs remain. Find the longest possible run of good rounds.	Hard8	Dynamic programmingArray+2	No attempts yet	2s	512 MB	Judgeable
SumdokuFill a 9x9 Sudoku grid so that constrained adjacent cells inside each 3x3 block satisfy <, =, or > versus 10, and print the lexicographically smallest solution.	Hard8	BacktrackingImplementation+1	No attempts yet	2s	512 MB	Judgeable
Ladder ManipulationGiven a ladder with N vertical lines, H rows, and M existing rungs, find the minimum number of rungs to add so every walk from column i ends at column i, or report -1 if more than 3.	Hard8	BacktrackingBrute force+2	No attempts yet	2s	512 MB	Judgeable
Snow BootsFor each of B boots with limits on snow depth and step length, decide whether the farmer can walk from tile 1 to tile N, landing only on tiles whose snow is shallow enough.	Hard8	Binary searchSorting+2	No attempts yet	2s	512 MB	Judgeable
XEN 3166Assign each country a length-K subsequence starting with its first letter so that code order matches name lexicographic order, or report impossible.	Hard8	GreedyString+1	No attempts yet	2s	512 MB	Judgeable
CitationsOrder the reading of a citation tree rooted at book 1 so that the sum of all book return times is minimized.	Hard8	TreeGreedy+2	No attempts yet	1s	1024 MB	Judgeable
Word ClockPlace n distinct words left to right on an h by w grid where words may share letters, or report that no placement exists.	Hard8	BacktrackingImplementation+2	No attempts yet	2s	512 MB	Judgeable
Amateur Radio NetworkSplit at least 4 points into two groups of size at least 2 minimizing the largest same-group pairwise distance, and output that diameter rounded up to 0.01.	Hard8	GeometryBinary search+2	No attempts yet	2s	512 MB	Judgeable
Grumpy Groundhogs in GridlandGiven N nested or disjoint burrow pairs on a line at depth 0, find the minimum maximum digging depth connecting only matched pairs, or report IMPOSSIBLE.	Hard8	GraphBFS+2	No attempts yet	2s	512 MB	Judgeable
Hiding MerlinDecompose a digit string into concatenated perfect squares, each at most 10 digits and starting with 1 to 9, and report the smallest possible total sum.	Hard8	String matchingDynamic programming+2	No attempts yet	4s	512 MB	Judgeable
I'm a FanFind the smallest CCW rotation angle whose swept orbit of a star-shaped polygon around the origin is a full disk.	Hard8	GeometryMath+2	No attempts yet	2s	512 MB	Judgeable
ParcelGiven n distinct integers and target w, decide whether four of them sum exactly to w.	Hard8	Two pointersHash map+1	No attempts yet	1s	512 MB	Judgeable
Harry the HamsterOn a directed weighted graph, Max and Min alternately choose the outgoing edge, Max moving first; compute the total travel time from s to t under optimal play.	Hard8	Game theoryDynamic programming+2	No attempts yet	3s	512 MB	Judgeable
Count the BitsGiven k and b, count the total number of 1-bits in all multiples of k from 0 to 2^b-1, and print the sum modulo 10^9+9.	Hard8	Dynamic programmingBit manipulation+1	No attempts yet	2s	512 MB	Judgeable
Maple Leaf StoryBind n skills of 2n to n keys so maximum quests each needing k skills all bound can be cleared. n <= 10, m <= 100.	Hard8	Brute forceCombinatorics+2	No attempts yet	1s	256 MB	Judgeable
cmpStore which of 12-bit buckets hold the remembered 12-bit value with 4095 bits, then read 12 prefix sums to binary search the bucket and compare it by a 12-bit count table to fit 20 memory accesses.	Hard8	Bit manipulationBinary search+2	No attempts yet	10s	256 MB	Judgeable
Bad KemingFill every gap in the spaced copy of S with chosen letters to make the longest prefix of S a contiguous substring, and find that prefix length.	Hard8	String matchingString+2	No attempts yet	2s	512 MB	Judgeable
Expression TreeGiven a binary expression tree with + and - operators, permute the operand values freely to maximize the evaluated result.	Hard8	TreeGreedy+2	No attempts yet	1s	256 MB	Judgeable
Shopping MallSimulate customers choosing the counter with the minimum total wait (lowest index on ties), then compute a weighted sum of membership numbers in the order customers leave.	Hard8	SimulationHeap+2	No attempts yet	1s	512 MB	Judgeable
NM and K (1)Choose exactly K non-adjacent cells from an N by M grid, at most 10 by 10, to maximize the sum of their values.	Hard8	Dynamic programmingBit manipulation+2	No attempts yet	2s	512 MB	Judgeable
Right-hand obstructionCars arrive in four queues at a crossroad; a front car passes only if the queue on its right is empty, so simulate second by second and report each car's crossing time or -1.	Hard8	SimulationQueue+2	No attempts yet	1s	512 MB	Judgeable
QuadtreeGiven a 2^n by 2^n binary matrix and a budget k, flip at most k entries so the resulting matrix has a quadtree with the fewest possible cells.	Hard8	TreeDynamic programming+2	No attempts yet	2s	512 MB	Judgeable
Universal and Existential QuantifiersGiven N half-open intervals whose union is [0,L), find the fewest intervals whose union is [0,L) and the fewest k such that any k intervals already cover [0,L).	Hard8	GreedySorting+2	No attempts yet	2s	512 MB	Judgeable
Computational IchthyologyAquariums in a row each spawn fish at times set by their population; Igor starts at tank 1, walks one tank per second, and must be present at each birth. Output the time of the first birth he misses.	Hard8	GreedySimulation+2	No attempts yet	2s	1024 MB	Judgeable
NamesGiven two strings, find the lexicographically largest string that is a subsequence of both, or print nothing if none exists.	Hard8	StringGreedy+1	No attempts yet	2s	1024 MB	Judgeable
String RemovalErase the whole string S using substring deletions that give scores or single-character deletions worth 1 point each, and find the maximum total score.	Hard8	Dynamic programmingString matching+2	No attempts yet	1s	512 MB	Judgeable
ConsulGiven N hidden votes, use point queries and value-count queries to find a candidate with strictly more than N/3 votes, or report that none exists.	Hard8	Divide and conquerBrute force+2	No attempts yet	1s	512 MB	Judgeable
Longest Increasing SequenceSplit a sequence into the maximum number of contiguous blocks whose sums form a strictly increasing sequence, and output the divider positions.	Hard8	Dynamic programmingPrefix sum+2	No attempts yet	5s	512 MB	Judgeable
TerrorGiven the sorted list of all pairwise distances among N houses on a line, reconstruct the actual positions with the first house fixed at 0.	Hard8	BacktrackingRecursion+2	No attempts yet	2.5s	1024 MB	Judgeable
GCD and Shortest PathIn a graph on 1..N where x and y are joined exactly when gcd(x,y)=1, count x with dist(x,K) equal to gcd(x,K).	Hard8	Number theoryGraph+2	No attempts yet	1s	1024 MB	Judgeable