372. Missax Info

Missax is more than a festival—it’s an immersive world where myth and modernity collide. Key elements include:

Sequence‑modification problems are central to many areas of computer science, ranging from bio‑informatics (e.g., DNA editing) to data cleaning and time‑series analysis. A common task is to delete the smallest possible set of elements so that the remaining subsequence satisfies a set of structural constraints.

The Missax problem was first introduced in the 2022 edition of the International Algorithmic Contest (IAC) as problem 372. The problem statement (re‑printed in Section 2) is deceptively simple, yet it captures a rich combinatorial structure: the hidden “missing axis’’ constraint forces the solution to avoid a family of intervals that are not explicitly given but can be inferred from the input.

Despite its simplicity, Missax resisted a naïve O(n²) dynamic‑programming solution for large inputs. Preliminary attempts using greedy heuristics failed to guarantee optimality. In this paper we: 372. Missax

The remainder of the paper is organised as follows. Section 2 restates the problem. Section 3 surveys related work. Section 4 presents the theoretical analysis, including the NP‑completeness proof and the parameter‑restricted algorithm. Section 5 details implementation choices and experimental results. Section 6 concludes and outlines future research directions.

Let

[ A = \langle a_1, a_2, \dots, a_n\rangle \qquad (a_i\in\mathbb Z) ] Missax is more than a festival—it’s an immersive

be a sequence of n integers.

A strictly monotone subsequence of A is a subsequence

[ B = \langle a_i_1, a_i_2, \dots, a_i_k\rangle,\qquad 1\le i_1 < i_2 < \dots < i_k\le n, ] The remainder of the paper is organised as follows

such that either

[ a_i_1<a_i_2<\dots<a_i_k\quad\text(strictly increasing) ]

or

[ a_i_1>a_i_2>\dots>a_i_k\quad\text(strictly decreasing) . ]

There are three primary reasons why 372. Missax has become a high-volume search term: