Inside the training routine of Croatia’s Sudoku elite

Competitive Sudoku asks for more than familiarity with the standard nine-by-nine grid. Every row and column must contain the digits one to nine, while the solver works against the clock, tracks incomplete cases and tries to recognise useful patterns without inventing false ones.

At Zagonetka.net, the Croatian Logic Association and its community of constructors regularly follow tournaments where those abilities are tested under pressure. National championships, continental events and international online competitions provide the competitive backdrop for a different kind of puzzle: improving the decisions that produce consistently fast and accurate solutions.

Miloš Kovač, one of Croatia’s leading competitive Sudoku solvers, has represented his country in national and international events. He is known for a methodical style based on candidate elimination, disciplined notation and short, focused training sessions rather than marathon attempts to solve every puzzle.

The conversation below has been lightly edited for clarity. Its practical lessons also suit Australian solvers, who can draw on puzzle pages in The Sydney Morning Herald and The Age, practice during train or tram journeys and join online events across the substantial time difference with Zagreb.

A week built around deliberate practice

What does a normal training week look like? Kovač begins with two easy puzzles and uses them to warm up his recognition of common configurations. These are not treated as routine filler. He checks whether he can identify the correct digit without hesitation, then moves to less predictable grids that require longer chains of candidate elimination.

His deeper sessions last between forty-five minutes and ninety minutes. A typical set includes two difficult Sudoku, one timed puzzle and a review of an old competition. He takes a short break between sets, keeping his attention sharp without stepping away from the logic for long.

“The important part is not the number of puzzles,” he says. “It is knowing why each decision was made. Twenty minutes of careful work can be worth more than an hour of guessing.”

Kovač records the time spent on each stage of a solve. If a grid takes too long because he missed a pair, that differs from one where he entered several candidates without checking the rest of the row. The distinction helps him direct the next session.

Candidates, notation and controlled speed

Candidate work lies at the centre of his method. Instead of filling every empty cell, Kovač places pencil marks only where more than one digit remains possible. He then scans boxes, rows and columns for a digit that has a single viable position or no viable position at all.

Speed drills use specially selected grids, with emphasis on clean elimination rather than rapid entry. This keeps his attention on the structure of the Latin square. A useful pattern should shorten a chain of reasoning, while a doubtful pattern can waste valuable seconds.

“Speed comes after control,” Kovač explains. “If you know exactly what you know, you can move quickly. If you are guessing, speed only makes the error arrive sooner.”

For timed practice, he varies the conditions. Some sessions include an early finish to encourage efficient scanning, while others replicate tournament scoring. He also experiments with visual notation and written candidates, choosing whichever produces the clearest record under pressure.

Learning from every wrong answer

Kovač keeps an error log divided into several categories: overlooked pairs, missed single candidates, incorrect pattern assumptions, transcription errors and premature time pressure. A wrong answer therefore becomes a specific piece of information rather than a vague feeling that the puzzle went badly.

After each major competition, he replays the difficult grids at a slower pace. He pauses whenever his original reasoning no longer works and attempts to locate the first unjustified decision. That moment is usually more instructive than simply discovering the corrected number.

He also compares his process with published solutions and discussion from the Croatian logic-puzzle community. “A solution can show the correct path, but the interesting question is why I left it,” he says. “The gap between those two things is where training has a purpose.”

Mistakes are not punished with extra grids. Kovač believes that excessive repetition can reinforce a weak habit. Instead, he changes one element in the next exercise, such as focusing exclusively on candidate pairs or solving without watching the clock.

Connecting Zagreb with Australian solvers

International online competitions have brought Kovač into regular contact with players from Australia. Despite the distance between Zagreb and cities such as Sydney and Melbourne, the shared puzzle language makes technical discussions surprisingly direct. A disputed placement can be examined cell by cell without either solver losing the thread.

The time difference is roughly eight to nine hours, depending on daylight saving. Calls may therefore take place early in the morning or late at night, while shared competitions often require Australian competitors to adjust their normal schedules. Kovač appreciates the discipline of these sessions because they expose him to unfamiliar styles of scanning.

Australian practice conditions also differ in useful ways. A solver can work through print grids during a train ride from outer Sydney or a tram journey across Melbourne, where phone screens offer less distraction. Print puzzles from Dymocks, discount bookshops and the puzzle-book aisles at stores such as Big W provide varied fonts and layouts.

“The paper reminds you to read every clue precisely,” Kovač says. “On a screen, it is easier to skip information because everything looks clean and permanent.”

Turning practice into tournament play

On competition morning, Kovač follows the same sequence he uses during ordinary training. He solves one straightforward grid, checks his notation, then completes a second puzzle at moderate speed. The session is short enough to sharpen concentration without creating the fatigue that can accompany overtraining.

During a timed Sudoku, he separates observation from entry. He first identifies the easiest placements and removes their implications from the candidate landscape. Only then does he commit digits to the grid. This reduces the temptation to rush a visible move while leaving a deeper contradiction unresolved.

The final minutes are reserved for verification. He scans completed rows and columns, reviews any cells containing several candidates and checks whether each box still contains nine different digits. Tournament scoring can reward speed, but a single avoidable error often costs more than the seconds saved.

Kovač credits the Croatian Logic Association and events shared through Zagonetka.net with making competition a communal pursuit rather than an isolated test. The competitive result matters, yet the useful lessons often come from studying another solver’s notation or discussing a grid after the clock stops.

His ambition is expressed in simple terms: “I want every session to leave one habit better than it was before. That can mean a cleaner pair, a steadier hand or a faster check. Progress is built from those small corrections, one grid at a time.”