Published by the Department of Computer Science, The University of Chicago.
Pascal Pfister
Institute of Theoretical Computer Science
ETH
Zurich, Switzerland
ppfister AT inf DOT ethz DOT ch
and
Angelika Steger
Institute of Theoretical Computer Science
ETH
Zurich,Switzerland
steger AT inf DOT ethz DOT ch
A random jigsaw puzzle is constructed by arranging $n^2$ square pieces into an $n \times n$ grid and assigning to each edge of a piece one of $q$ available colors uniformly at random, with the restriction that touching edges receive the same color. We show that if $q = o(n)$ then with high probability such a puzzle does not have a unique solution, while if $q \ge n^{1 + \varepsilon}$ for any constant $\varepsilon > 0$ then the solution is unique. This solves a conjecture of Mossel and Ross ( Shotgun assembly of labeled graphs, arXiv:1504.07682).
Submitted October 21, 2017, revised May 22, 2017, in final form June 29, 2017
published June 30, 2017.