FROM LEARNING TO COMPETING

Expert.
Put your skills to the test.

Bulgarian Informatics Group A · 2007–2026

274 independently explained problems: 54 Municipal, 54 Regional, 109 National Olympiad and 57 Autumn Tournament tasks. Difficulty labels are learning estimates, not official ratings. Some events share Senior/IATI or Group A/B problem sets. Special formats, scoring limitations and source clarifications are explained on affected tasks. Existing shared National-round problems keep their permanent URLs.

Search by name or topic

Round / tournamentYearContent

Easy15

Graph dynamic programming 1

Difference arrays 1

Complement graphs 1

Constraint propagation 1

Dynamic programming 1

Two-dimensional prefix sums 1

Canonical forms 1

Parsing 1

Sparse aggregation 1

Binary search 1

Frequency counting 1

Sorting and aggregation 1

Cycle detection 1

Polygon area 1

Stack simulation 1

Medium75

Integer partitions 1

Breadth-first search 1

Divisors 1

Prime sieve 1

Subset dynamic programming 1

Interval dynamic programming 2

Bitwise XOR 1

Integer search 1

Euler tours 1

Dynamic programming 1

Heaps 1

Projection geometry 1

Multidimensional prefix sums 1

Z algorithm 1

Grid dynamic programming 1

Maximum spanning forests 1

Stacks 1

Digit counting 1

Functional graphs 1

Parity disjoint sets 1

Sorting 1

Fenwick order statistics 1

Coordinate transformations and simulation 1

Sliding window & DP 1

Stern-Brocot tree 1

Ordered sets 1

Interactive bit recovery 1

Combinatorial ranking 1

Geometry 4

Number theory 1

Monotonic stack 1

Dynamic programming 5

Prime sieve 1

Digit dynamic programming 1

Lattice geometry 1

Computational geometry 1

DAG dynamic programming 1

Prefix maxima 1

Bitmask dynamic programming 1

Convex hull 1

Greedy representation and compressed binary arithmetic 1

Matrix exponentiation 1

Greedy bounds 1

Big integers 1

Monotonic deque 1

Parsing 1

Order constraints 1

Finite-state dynamic programming 1

Mathematical indexing 1

Constructive algorithms 1

Greedy scheduling 1

Counting 1

Game theory 1

Monotonic stack 1

Dijkstra 1

Divisor sieve 1

Inclusion-exclusion 2

Dynamic programming 1

Permutation cycles 1

Tree centers 1

Euler totient sieve 1

Lattice geometry 1

Modular construction 1

Two pointers 1

Periodic impartial games 1

Digit counting 1

Hard120

Value-set dynamic programming 1

Constructive optimization 1

XOR construction 1

Geometry optimization 1

Diophantine equations 1

Monotone stack 1

Computational geometry 1

Small-to-large ordered-set merging 1

Tree DP with minimum start depth 1

Periodic histogram rectangles 1

Vandermonde identity 1

Dominance cuts 1

DFS & ordered sets 1

Segment-tree graph and Dijkstra 1

Square-root decomposition 1

Meet in the middle 1

Segmented sieve 1

Potential-based recoloring 1

Binary lifting on bit states 1

Compressed suffix GCDs 1

Dynamic programming by last value 1

Successor disjoint sets 1

Layered breadth-first search 1

Bipartite matching 1

Offline heavy/light decomposition 1

Sweep line 1

Tree binary lifting 1

Bellman–Ford & zero cycles 1

Rectangle nesting sweep 1

Interval dynamic programming 1

Topological sorting 1

KMP borders & expected waiting time 1

Interactive topological sorting 1

Monotone stack and DAG 1

Combinatorial recurrence 1

Difference arrays and Fenwick tree 1

Matrix segment tree 1

Constructive XOR sequences 1

Dynamic programming 1

Duval algorithm and Lyndon words 1

Cached comparison sorting 1

Matrix exponentiation 2

Upper convex hull tangents 1

Heavy-light decomposition and path maxima 1

Greedy path decomposition 1

Lexicographic topological ordering 1

Vertex-disjoint paths 1

Tree rerooting 1

Incremental bipartite matching 1

Partition dynamic programming 1

Lowest common ancestor 1

Suffix array and LCP 1

Gaussian elimination over a finite field 1

Multiset reconstruction 1

Rectangle dynamic programming 1

Decision-tree capacity DP 1

Flow and binary search 1

Exact rational backtracking 1

De Bruijn graph and Euler trails 1

Inclusion–exclusion & linear sieve 1

Euler totient and divisors 1

Computational geometry 1

Digit dynamic programming 1

Permutation parity 1

Möbius inversion 1

Aho–Corasick and KMP 1

Path-integrated updates 1

Bounded precomputation 1

Constraint propagation 1

Articulation points and binary search 1

Polynomials & offline queries 1

Randomized candidate elimination and binary search 1

Expected value and algebra 1

Convex hull trick with block rebuilding 1

Interval invariants and construction 1

Longest common subsequence and block decomposition 1

Dominance ordering and chain decomposition 1

Meet in the middle and fixed-weight bitmasks 1

Sweep line and lazy segment tree 1

Lagrangian relaxation and Monge optimization 1

Substring ranking 1

Convex dynamic programming 1

Bridges 1

Sweep line dynamic programming 1

2-SAT with segment-tree implications 1

Dynamic programming 1

Two-dimensional range maximum 1

Integer geometry 1

Euler trails 1

Large integer arithmetic 1

Convex rearrangement 1

Meet in the middle 1

Continuity and bisection 1

Geometry and binary search 1

Histograms and interval DP 1

Bitmask game dynamic programming 1

Range minimum queries 1

Polynomial construction 1

Heavy-light counting 1

Bitsets and short cycles 1

Walsh–Hadamard transform and linear basis 1

Monotonic stack and offline queries 1

Sweep line and binary search 1

Pairing strategies and modular arithmetic 1

Offline sweep and Fenwick tree 1

Bipartite matching strategy 1

Exact convex hull of reciprocal speeds 1

Bitwise constraint propagation 1

Suffix automaton 1

Euler tour and parity 1

Bellman-Ford and binary search 1

Counting matchings on paths 1

Greedy heap 1

Sweep line 1

Functional graph 1

Greedy finite trajectory coverage 1

Persistent lazy segment tree 1

Scored geometric clustering 1

Reverse DSU and tree diameters 1

Very hard64

Greedy contraction & priority queue 1

Transfer matrices 1

Interactive divide and conquer 1

Geometric coverage 1

Monge dynamic programming 1

Function monoid & lazy segment tree 1

Periodic digit arithmetic 1

String dynamic programming 1

Number theory enumeration 1

Aliens optimization and convex hull trick 1

SCC counting and polynomial convolution 1

Fenwick tree and convex hull DP 1

Cartesian tree and small-to-large treaps 1

Convex hull trick 1

Minimum-cost flow 1

Layered 0–1 BFS in a stack language 1

Lazy segment trees by digit length 1

Heavy-light decomposition and lazy assignment 1

Bitmask Kruskal 1

Interactive periodicity 1

Algebraic scored construction 1

Lipschitz branch and bound 1

Geometry and compressed walk counting 1

Offline subset sums and blocked bit ranks 1

Implicit Dijkstra and segment trees 1

Bipartite matching 1

Sweep line 2

Constructive geometry 1

Cactus graph 1

Diagonal sweep with active corners 1

Dynamic connectivity 1

Bit DP with addition carries 1

Matrix Exponentiation 1

Shortest Paths 1

Computational Geometry 1

Ghost trajectories and binary search 1

Suffix array and reverse processing 1

Tree coverage dynamic programming 1

Linear greedy skyline 1

Counterfactual regret minimization 1

Information-state search 1

Interactive elimination 1

Finite-state randomness recycling 1

DFS graph encoding 1

Bayesian Monte Carlo 1

Computational Geometry 2

Convex envelope search 1

Persistent heapsort 1

Graph Algorithms 1

Bipartite Matching 1

Convex Hull Trick 1

Interactive Algorithms 1

Constructive Algorithms 1

Dynamic Programming 1

Graph Connectivity 1

Gray-code cycle construction 1

Dynamic next-greater elements 1

Dynamic Euler-tour aggregates 1

Geometric construction 1

Communication protocol 1

Leaf intervals and rectangle sweep 1

Persistent convex hull 1

Try the problem yourself before reading the analysis. Solutions use C++17. Special grader headers and compiler requirements are explained on affected tasks.

{ }

Choose your next challenge.

Choose a difficulty folder, then a problem. Each task includes an English summary, worked example, solution analysis and commented C++17 code.

GROUP AEASY → VERY HARDC++17

Expert.Put your skills to the test.

Choose your next challenge.

Choose your next challenge.

Expert.
Put your skills to the test.