372. Missax May 2026

Each node stores a pair

[ (\ell, v) \quad\textwhere \ell\text is the length of a feasible subsequence ending with value v. ]

The tree is ordered by v. Additionally, we augment each node with the maximum length in its subtree, enabling range‑maximum queries (RMQ). 372. Missax

Missax occurs biennially and is invitation-only, with applications accepted via a cryptic online riddle. Prospective attendees are advised to:

Rumors swirl about a clandestine group within the festival, known only as The Curators. Allegedly responsible for Missax’s enigmatic design, they operate from a hidden chamber called the “Vault of 372,” referencing the festival’s ancient origin date. While organizers deny its existence, many point to recurring symbols in the festival—spirals, three-star patterns, and riddles etched into lanterns—as clues left by this elusive collective. Each node stores a pair [ (\ell, v)

Missax has influenced a new wave of storytelling and community activism. Its philosophy of “collective creation” has inspired grassroots movements, such as the Missax Youth Initiative, which teaches young creators to blend technology and folklore.

The festival also sparked academic interest. In 2023, Oxford University hosted a symposium analyzing how Missax’s rituals mirror ancient rites in Mesopotamia and Mesoamerica, deepening its mythic allure. Rumors swirl about a clandestine group within the

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:

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.