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Bulgarian Informatics Group B · 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 Junior/IATI or Group A/B problem sets. Special formats, scoring limitations and source clarifications are explained on affected tasks. The two previously featured Autumn problems keep their existing permanent URLs.

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Round / tournamentYearContent

Easy46

Geometry 1

Geometry & formulas 1

Strings 1

Prefix balance 1

Interval distance 1

Array extrema 1

Distance to a rectangle 1

Sieve 1

Reachability DP 1

Interval union 1

Breadth-first search 1

Sparse counting 1

Subarray counting 1

Expression parsing 1

Big integers 1

Exhaustive hypothesis checking 1

Modular arithmetic 1

Dynamic programming 4

Enumeration 1

Frequency counting 1

Board simulation 1

Two pointers 1

Binary search 2

Permutation adjacency 1

Recurrences & base three 1

Two pointers 1

Sorting & contributions 1

Acyclic orientation by a total vertex order 1

Prime numbers 1

Unbounded knapsack 1

Counting contributions 1

Tree traversal 1

Unbounded knapsack 1

Inversions and parallel swaps 1

Game dynamic programming 1

Binary search on answer 1

Algebraic aggregation 1

Sweep line and closed intervals 1

Flood fill 1

Prefix XOR 1

Matrix exponentiation 1

Disjoint set union 1

Medium94

BFS & shortest paths 1

DFS & reachability 1

Permutations 1

Backtracking 1

Enumeration 2

Knapsack 1

Disjoint sets 1

Breadth-first search 2

Coordinate compression 1

Big integers 1

Disjoint set union 1

Dynamic programming 1

Greedy coverage 1

Persistent stack 1

Normalized directions 1

0-1 BFS 1

Dynamic programming 1

Heaps 1

Two-dimensional knapsack 1

Multidimensional prefix sums 1

Circular intervals & sweep line 1

Counting tree embeddings 1

Dynamic programming 1

Subset sum 1

Topological sorting 1

Binary search 1

Z algorithm 1

Grid dynamic programming 1

Pythagorean triples 1

Prefix sums & integer search 1

Greedy scheduling 1

Algebraic enumeration 1

Gray code 1

Stacks 1

Prime sieve 1

Subsequence dynamic programming 1

Monotonic stack and DP 3

Digit counting 1

Bitsets 1

Functional graphs 1

Fenwick tree counting 1

Parity disjoint sets 1

Extended Euclidean algorithm 1

Longest bitonic subsequence 1

Prefix parity 1

Sorting 1

Remainder automata 1

Monotone stacks & DAG DP 1

Prefix sums 1

Rank dynamic programming 1

Offline dominance counting 1

Divisor sieve and Kruskal 1

Interval dynamic programming 1

Suffix enumeration 1

Fenwick order statistics 1

Sweep line 2

Weighted subsequence dynamic programming 1

Primitive lattice directions 1

Sliding window & DP 1

Bitwise subarray counting 1

Stern-Brocot tree 1

Subset dynamic programming 1

Number bases and counting 1

Binary search and greedy subset coverage 1

Divisor sieves and independent point-change queries 1

Ordered sets 1

Sorting and two pointers 1

Triangle inequality & prefix minima 1

Meet in the middle 1

Tree metrics and minimum spanning tree 1

Computational geometry 1

Interactive bit recovery 1

Earliest deadline scheduling 1

Constrained ballot-path dynamic programming 1

DAG dynamic programming 1

Sorting and longest nondecreasing subsequence 1

Pigeonhole principle and repeated prefix differences 1

Prefix maxima 1

Priority queue merging 1

GCD and game invariants 1

Convex hull 1

Shortest paths with a budget state 1

Euler tours and connected components 1

Ternary state dynamic programming 1

Game theory 1

Segment intersection & DSU 1

Palindrome dynamic programming 1

Memoized game states and big integers 1

Dynamic programming & monotonic queues 1

Hard96

Diophantine equations 1

Tree rerooting 1

Rectangle nesting sweep 2

Monotone stack 1

Implicit graph reachability 1

Expression trees 1

Computational geometry 1

DFS & ordered sets 1

Tree path decomposition 1

Number theory 1

Bipartite matching 1

Offline heavy/light decomposition 1

Sweep line 2

Tree binary lifting 1

Bellman–Ford & zero cycles 1

Truncated big integers 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

Convex optimization 1

Difference arrays and Fenwick tree 1

Euler trail decomposition 1

Matrix segment tree 1

Dynamic programming 1

Cached comparison sorting 1

Matrix exponentiation 1

Combinatorial unranking 1

Upper convex hull tangents 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

Monotonic stack 1

Multiset reconstruction 1

Extended Euclid and factored output 1

Rectangle dynamic programming 1

Flow and binary search 1

Inclusion–exclusion & linear sieve 1

Euler totient and divisors 1

Stars and bars and composite moduli 1

Computational geometry 1

Digit dynamic programming 1

Permutation parity 1

Monotone stacks & binary lifting 1

Möbius inversion 1

Aho–Corasick and KMP 1

Prefix/suffix maxima and forced records 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

Aggregate queues and two pointers 1

Median queries on two sorted position lists 1

Length and resource dynamic programming 1

Hybrid segmented prime sieve 1

Tournament winner tree with grader comparisons 1

Two-dimensional range maximum 1

Divide and conquer with a comparison oracle 1

Global min-cut by repeated maximum flow 1

Convex rearrangement 1

Bitmask game dynamic programming 1

Range minimum queries 1

2D prefix sums and monotone scanning 1

Polynomial construction 1

Backtracking and offline tabulation 1

Heavy-light counting 1

Bitsets and short cycles 1

Recursive interval aggregation 1

Grid boundaries and rectangle scanning 1

Shortest paths on residues 1

Ordered lower envelope and exact area updates 1

Convex clipping and inclusion–exclusion 1

Tree path compression 1

Expression interval dynamic programming 1

Ordered bus-assignment dynamic programming 1

Sweep line and binary search 1

Event simulation with a heap and linked list 1

Offline sweep and Fenwick tree 1

Bipartite matching strategy 1

Greedy finite trajectory coverage 1

Tree DP and invisible-pawn search 1

Permutation parity and constructive cycle splicing 1

Divide and conquer on residue classes 1

Offline stack queries 1

Strong components and a two-tree failure certificate 1

Very hard38

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

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 1

Constructive geometry 1

Cactus graph 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

Convex envelope search 1

Persistent heapsort 1

Dynamic Euler-tour aggregates 1

Geometric construction 1

Communication protocol 1

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

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