The Height and Size of Random Hash Trees and Random Pebbled Hash Trees

  • Authors:
  • Luc Devroye

  • Affiliations:
  • -

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 1999

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Abstract

The random hash tree and the N-tree were introduced by Ehrlich in 1981. In the random hash tree, n data points are hashed to values X1, . . . , Xn, independently and identically distributed random variables taking values that are uniformly distributed on [0,1]. Place the Xi's in n equal-sized buckets as in hashing with chaining. For each bucket with at least two points, repeat the same process, keeping the branch factor always equal to the number of bucketed points. If Hn is the height of tree obtained in this manner, we show that Hn/log2 n \to 1 in probability. We also show that the expected number of nodes in the random hash tree and random pebbled hash tree is asymptotic to 2.3020238 . . . n and 1.4183342. . . n, respectively.