FROM LEARNING TO COMPETING

Beginner.
Your first challenges.

Bulgarian Informatics Group E · 2007–2026

270 independently explained problems: 54 Municipal, 54 Regional, 105 National Olympiad tasks and 57 Autumn Tournament tasks. Start with the easier tasks and work upwards. Difficulty labels are learning estimates, not official ratings; Group E also includes challenging national-level problems. Years follow Arena’s competition-season labels. Source clarifications are noted on affected tasks.

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Round / tournamentYearContent

Easy149

Loops & simulation 26

Greedy 1

String parsing 1

Bitmask enumeration 1

Time arithmetic 1

Intervals 2

Exhaustive search 1

Counting 9

String checks 1

Running maximum 2

Sorting 5

Intervals 1

String construction 1

Digit patterns 1

Time arithmetic 1

Inverse operations 1

Unit conversion 1

Integer arithmetic 5

Comparisons 1

Running minimum 1

String parsing 1

Simulation 1

Geometry 1

Reverse simulation 1

Conditions 1

Enumeration 1

Conditional logic 1

Nested loops & patterns 1

String scanning 1

Intervals & counting 1

Strings & digits 2

Intervals & counting 1

Arrays & differences 1

Greedy comparison 1

Integer arithmetic 1

Counting 1

Counting formulas 2

Loops & modulo 1

String filtering 1

Enumeration 2

Sorting & geometry 1

Minima & maxima 1

Time arithmetic 4

Digits & comparison 1

Digit checks 1

Digit replacement 1

String scans 1

Streaming minimum & maximum 1

Loops & simulation 6

String scans 1

Frequency counting 1

Strings & sorting 1

Strings & scoring 1

Integer arithmetic 1

Running state 1

Sorting 1

Modular simulation 1

Exhaustive cases 1

Pattern reasoning 1

Prefix balances 1

Counting & frequencies 1

Digits & enumeration 1

Case analysis 1

Periodic counting 1

Circular distance 1

Digit arithmetic 1

Time simulation 1

Digits & arithmetic 1

Prefix sums & tie breaking 1

Arrays & simulation 1

String runs 1

Parity 1

Calendar simulation 1

Grids & bounds 1

Expression parsing 1

Binary representation 1

Digit prefix sums 1

Ceiling division & money 1

Time simulation 1

Bounded enumeration 1

Counting & filtering 1

String conversion 1

Occupancy arrays 1

Integer arithmetic 1

GCD & LCM 1

Presence tracking 1

GCD & LCM 1

Set bounds 1

State simulation 1

Expression parsing 1

Conservation of flow 1

GCD & LCM 1

Division with remainder 1

Grid neighbors 1

Medium96

Arithmetic 1

Piecewise arithmetic 1

Dynamic programming 1

Exhaustive search 1

Parsing & run-length encoding 1

Time arithmetic 2

Binary search 1

Counting multiples 1

Independent greedy choices 1

Greedy digit construction 1

Arithmetic progressions 1

Integer arithmetic 2

Arrays & scoring 1

Divisibility & GCD 4

Strings & runs 2

Loops & simulation 1

Loops & simulation 9

Counting formulas 3

Sorting & sets 1

Case analysis 1

Subset dynamic programming 2

State machines 1

Sequence simulation 1

Bounds & greedy 1

Binary search 1

Set elimination 1

Time & simulation 1

Greedy purchasing 1

Greedy counting 1

GCD & LCM 1

Greedy counting 2

Array scanning 1

Exhaustive search 1

Prime factors 1

Pattern reasoning 2

Prefix sums 2

Time & filtering 1

Runs & streaming 1

Decimal arithmetic 1

Number patterns 1

Exhaustive search 2

Parity counting 1

Time simulation 1

Calendar simulation 1

Bounded enumeration 1

Ratios & limiting resources 1

Two pointers 1

Time rounding 1

Running state 1

Geometry & greedy bounds 1

Circular intervals 1

Dynamic programming 1

Remainder counting 1

Algebra & enumeration 1

Prefix counts 1

Round simulation 1

Interval overlap 1

Prefix & suffix sums 1

Periodic sequences 1

Difference arrays 1

Queue simulation 1

Grid geometry 1

Primes & search 1

Running maximum 1

Sliding windows 1

Prime sieve 1

Arrays & simulation 1

Enumerating capacity 1

Time & exhaustive search 1

Prime factorization 2

Inclusion–exclusion 1

Factorization & simulation 1

Number theory 1

Hard23

GCD, LCM & parity 1

Prefix sums 1

Enumeration 1

Counting & frequencies 1

Greedy construction 2

Binary search 1

Two pointers 1

Sliding windows 1

Divisor sums & factorization 1

Geometry & money 1

GCD & divisors 1

Nested simulation 1

Pair enumeration 1

Frequency simulation 1

Two pointers 1

Frequency counting 1

Binary search 1

Palindrome generation 1

Dynamic programming 1

Interval reconstruction 1

Periodic counting 1

Number theory 1

Very hard2

Compressed suffix GCDs 1

Meet in the middle 1

Try the problem yourself before reading the analysis. Every solution uses standard C++17 headers.

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Start with a small challenge.

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

GROUP EEASY → VERY HARDC++17

Beginner.Your first challenges.

Start with a small challenge.

Start with a small challenge.

Beginner.
Your first challenges.