We describe the algorithms used by the ETH Flippers team in the CG:SHOP 2026 Challenge. Each instance consists of a set of triangulations on a common point set, and the objective is to find a central triangulation that minimizes the total parallel flip distance to the input set. Our strategy combines an exact solver for small and medium-sized instances with a suite of heuristics for larger instances. For the exact approach, we formulate the problem as a SAT instance with XOR clauses to model edge transitions across multiple rounds, further optimized by lower bounds derived from exact pairwise distances. For larger instances, we use a greedy local search and edge-coloring techniques to identify maximal sets of independent flips. Our approach ranked second overall and first in the junior category, computing provably optimal solutions for 186 out of 250 instances.

翻译：本文描述了ETH Flippers团队在CG:SHOP 2026挑战赛中使用的算法。每个实例由共点集上的若干三角剖分组成，目标是找到一个与输入集总并行翻转距离最小的中心三角剖分。我们的策略结合了面向中小型实例的精确求解器和面向较大实例的启发式算法套件。在精确求解方法中，我们将问题形式化为包含XOR子句的SAT实例以建模多轮边缘转换，并通过精确成对距离推导的下界进一步优化。对于较大实例，我们采用贪心局部搜索和边染色技术来识别最大独立翻转集。我们的方法在总排名中位列第二，并在初级组中排名第一，为250个实例中的186个计算出了可证明最优解。