Mittagsseminar (in cooperation with A. Steger, D. Steurer and B. Sudakov)

Date and Time: Thursday, November 17, 2011, 12:15 pm

Duration: 30 minutes

Location: OAT S15/S16/S17

Speaker: Thomas Rast

Pancake flipping is NP-hard

Assume a stack of pancakes can only be sorted (by size) by inserting a spatula between two pancakes, and flipping the entire upper part of the stack. This is formally known as sorting by prefix reversal (SBPR). The question for the number of reversals needed has been open since 1975.

There is a "natural" efficient sequence of flips in which some SBPR instances can be solved, giving rise to a lower bound. In a very recent arXiv paper, Bulteau, Fertin and Rusu show that deciding whether a given instance attains this lower bound is NP-hard. Thus more generally, determining the number of flips needed is NP-hard.

I will give an overview of the problem and known results, and then show some details of the (rather surprising at least for me) reduction from 3-SAT.

Upcoming talks     |     All previous talks     |     Talks by speaker     |     Upcoming talks in iCal format (beta version!)

Previous talks by year:   2024  2023  2022  2021  2020  2019  2018  2017  2016  2015  2014  2013  2012  2011  2010  2009  2008  2007  2006  2005  2004  2003  2002  2001  2000  1999  1998  1997  1996  

Information for students and suggested topics for student talks

Automatic MiSe System Software Version 1.4803M   |   admin login