Discrete & Computational Geometry

, Volume 35, Issue 1, pp 131–141 | Cite as

Polygons Needing Many Flipturns

  • Therese BiedlEmail author


A flipturn on a polygon consists of reversing the order of edges inside a pocket of the polygon, without changing lengths or slopes. Any polygon with n edges must be convexified after at most (n − 1)! flipturns. A recent paper showed that in fact it will be convex after at most n(n−3)/2 flipturns.We give here lower bounds.We construct a polygon such that if pockets are chosen in a bad way, at least (n − 2)2/4 flipturns are needed to convexify the polygon. In another construction, (n −1)2/8 flipturns are needed, regardless of the order in which pockets are chosen. All our bounds are adaptive to a pre-specified number of distinct slopes of the edges.


Computational Mathematic Distinct Slope 
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Copyright information

© Springer 2005

Authors and Affiliations

  1. 1.School of Computer Science, University of Waterloo, Waterloo, Ontario, N2L 3G1Canada

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