Covering a square with n equal discs
Place n points in the unit square to minimize the maximum distance r from any point of the square to its nearest placed point; equivalently, cover the unit square with n equal discs of shared radius r and minimize r.
Formal definition
- ContainerThe closed unit square [0, 1] × [0, 1], with lower-left corner (0, 0) and upper-right corner (1, 1)
- SubmissionExactly n distinct points, each coordinate a decimal string with at most nine places
- Scorer(P) is the maximum over the square of the distance to the nearest submitted point. The verifier computes its exact rational square and rounds the square root upward at 10⁻¹⁸, guaranteeing a valid covering radius
- Why this is finiteWithin each point's Voronoi cell, the convex function |x − p|² attains its maximum on a convex polygon at a vertex. The continuous maximum therefore reduces to checking finitely many rational Voronoi vertices in exact arithmetic
- ObjectiveMinimize r(P) over all valid point sets P
Getting a feel for it
Contrast with circle packing
Circle packing forbids overlap and keeps centres at least one radius away from the boundary; covering allows discs to overlap and protrude beyond the edges, making the four corners the primary bottlenecks. For the same n, optimal coverings and optimal packings have very different structures.
Literature results and open cases
Kershner proved in 1939 that the regular hexagonal lattice gives the thinnest covering of the infinite plane, but the boundary and corners of a square break lattice symmetry. Optimal coverings are proved for n = 5 and n = 7; n = 6 and n = 8–30 feature the best constructions from the literature (reconstructed as verifiable coordinates from the vector figures in report HUT-TCS-A62), while n = 31–35 remain open without publicly reproducible coordinates.
SourceCurrent best solutions by n
Each parameter n is an independently scored sub-problem. Select any card to inspect the current record construction or submit a stronger solution.
Discussion (1) ↓Data and citation
All sub-problems in this family — authoritative scores, proof status, coordinates, and sources — are published at the stable URL below under CC BY 4.0. Because scores update as records fall, please cite the file's generatedAt timestamp.
GET https://minmaxarena.com/data/circles-covering-a-square.json
Cite the frozen 2026-10 edition: live records change, whereas a frozen edition stays fixed and reproducible.
GET https://minmaxarena.com/data/editions/2026-10/circles-covering-a-square.json
BibTeX (click to copy)
@misc{minmaxarena-circles-covering-a-square-2026-10,
title = {{Covering a square with n equal discs} (P73)},
author = {{MinMax Arena}},
year = {2026},
note = {Machine-verified records, 2026-10 edition},
url = {https://minmaxarena.com/data/editions/2026-10/circles-covering-a-square.json},
license = {CC BY 4.0}
}Discussion
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Grouped by player and sub-problem, showing the latest note first. Earlier versions and replies are preserved; click any note to read or reply. Notes can be published alongside record-breaking submissions.