Subtasks

The concept of subtasks was first formally introduced in IOI 2010. The idea is basically to split a problem into two or more smaller problems with gradually increasing difficulty, and assign them different points.

For example:

Subtask 1 (20 points)

• N = 1
• 1 ≤ K ≤ 100

Subtask 2 (20 points)

• 1 ≤ N ≤ 100
• K = 1

Subtask 3 (60 points)

• 1 ≤ N ≤ 100
• 1 ≤ K ≤ 100

In this type of problem, you won't be writing a Constraints() method. Instead, you will be writing SubtaskX() methods, where X is the subtask number.

info

As of this version, you can define up to 25 subtasks: Subtask1() .. Subtask25().

Subtask definitions

A subtask is basically just a set of constraints. It can be specified by the method SubtaskX(), where X is the subtask number. Inside the method, the constraint specifications are given, similar to what you usually do in the Constraints() method. Points for each subtask can be given using Points() method, that takes a floating-point number argument as the points.

Thus, the above example can be implemented as:

void Subtask1() {
    Points(20);

    CONS(N == 1);
    CONS(1 <= K && K <= 100);
}

void Subtask2() {
    Points(20);

    CONS(1 <= N && N <= 100);
    CONS(K == 1);
}

void Subtask3() {
    Points(60);

    CONS(1 <= N && N <= 100);
    CONS(1 <= K && K <= 100);
}

Global constraints

It is possible to specify a set of constraints that apply to every subtask, via the Constraints() method. For example, we can extract common constraints in the above example as follows:

void Constraints() {
    CONS(1 <= N && N <= 100);
    CONS(1 <= K && K <= 100);
}

void Subtask1() {
    Points(20);

    CONS(N == 1);
}

void Subtask2() {
    Points(20);

    CONS(K == 1);
}

void Subtask3() {
    Points(60);

    // no additional constraints
}

Test groups

If your problem has subtasks, you will be writing test groups, not test cases.