Overhang

  • Authors:
  • Mike Paterson;Uri Zwick

  • Affiliations:
  • University of Warwick, United Kingdom;Tel Aviv University, Tel Aviv, Israel

  • Venue:
  • SODA '06 Proceedings of the seventeenth annual ACM-SIAM symposium on Discrete algorithm
  • Year:
  • 2006
  • Jenga

    SODA '02 Proceedings of the thirteenth annual ACM-SIAM symposium on Discrete algorithms

  • Concrete Math

    Concrete Math

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Abstract

How far off the edge of the table can we reach by stacking n identical blocks of length 1? A classical solution achieves an overhang of 1/2Hn, where Hn = Σni=1 1/i ~ ln n is the nth harmonic number, by stacking all the blocks one on top of another with the ith block from the top displaced by 1/2i beyond the block below. This solution is widely believed to be optimal. We show that it is exponentially far from optimal by giving explicit constructions with an overhang of Ω(n1/3). We also prove some upper bounds on the overhang that can be achieved. The stability of a given stack of blocks corresponds to the feasibility of a linear program and so can be efficiently determined.