Using hashing to solve the dictionary problem

We consider the dictionary problem in external memory and improve the update time of the wellknown buffer tree by roughly a logarithmic factor. For any λ ≥ max{lg lg n, logM/B(n/B)}, we can support updates in time O( λ B ) and queries in time O(logλ n). We also present a lower bound in the cell-probe model showing that our data structure is optimal. In the RAM, hash tables have been use to solve the dictionary problem faster than binary search for more than half a century. By contrast, our data structure is the first to beat the comparison barrier in external memory. Ours is also the first data structure to depart convincingly from the indivisibility paradigm. 

• Type: Journal
• Year: 2012
• Where: SODA
• Authors: John Iacono, Mihai Patrascu
• Keywords: Algorithms, Cell Probe Model, Dictionary Problem, Hash Tables, SODA 2012