NOI Singapore Preparation: National Olympiad Informatics

Five hours, four to five tasks

The National Olympiad in Informatics is modelled after the International Olympiad in Informatics. The first NOI was hosted by the School of Computing at the National University of Singapore in 1998, and the School of Computing has hosted it annually since.

The format is serious: a five-hour session in which each contestant individually solves and programs a solution to each of four to five programming tasks. Solutions are judged on correctness and on the resources used, producing answers within time, memory and other limits.

The competition is divided into two contests — a preliminary and a final — so preparation has to target both rather than treating the first as a formality.

Five hours changes what is tested

This is the single most important thing to understand before preparing.

A 45-minute contest rewards recognising a problem type quickly. A five-hour contest with four or five substantial tasks rewards something else entirely: sustained concentration, the ability to debug under pressure, and the judgement to decide which task deserves the next hour.

Students who have only done short contests find the first full-length practice session genuinely exhausting, and that is the point of running them. Stamina is trainable and nobody arrives with it.

Resources are judged, not just correctness

Solutions are judged on correctness and the resources used, within time, memory and other limits. A program that produces the right answer too slowly does not score fully.

So estimating cost before writing is part of the work rather than an afterthought. How many operations will this approach take on the largest permitted input? Does this data structure fit in memory? A student who writes first and measures later loses the time they needed for the next task.

Subtask strategy

IOI-style tasks typically award marks for solving restricted versions of the problem — smaller inputs, special cases, simplified constraints.

That makes the right opening move on a hard task frequently to write the obvious slow solution, bank the subtask marks, and only then consider whether a faster approach is worth the remaining time.

Students who hold out for the full solution on every task routinely score less than students who banked partial marks across all of them. Planning that allocation across five hours is a skill we practise explicitly.

What the tasks require

Dynamic programming is the most important single technique at this level and decides most mid-paper tasks. States, transitions and the order of computation.

Graphs and traversal — representation, breadth and depth first search, shortest paths, connectivity — applied to tasks that rarely announce themselves as graph problems.

Greedy algorithms, with the discipline of proving the exchange argument rather than assuming the obvious choice works.

Sorting, searching and fluent use of the standard library, including binary search on an answer, which recurs constantly.

Who can enter

Contestants must currently attend a local junior college or secondary school, which applies regardless of nationality or citizenship. Singaporean permanent residents or citizens residing overseas who attend an equivalent school are also eligible.

For students outside Singapore who cannot enter, the past tasks remain among the best available training for any IOI-route olympiad, and we use them with students preparing for INOI and USACO.

Where it sits among the alternatives

NOI is considerably more demanding than the entry-level contests. A Class 9 student should normally reach it through something shorter first.

The Canadian Computing Competition Junior division is three hours and five problems, which is a sensible step down. The Australian Informatics Olympiad is three hours and six questions. Either builds the technique NOI then tests at greater length.

Students not yet programming should start with CAT or Bebras, neither of which requires code.

How the classes run

Live online group classes, maximum eight students, with code written and submitted during the session against real test data.

Full five-hour practice contests run in the closing months, because the only way to prepare for a five-hour contest is to sit five-hour contests. Sessions afterwards review how time and attention were distributed rather than only which tasks were solved.

Eligibility, contest structure and selection arrangements are set by the organisers each year. Confirm the current details with the NUS School of Computing before planning around them.