_:n161124605ad34361b39f60f438a67c26xb23
<http://schema.org/description>
"A minimal perfect hash function bijectively maps a key set S out of a\nuniverse U into the first |S| natural numbers. Minimal perfect hash\nfunctions are used, for example, to map irregularly-shaped keys, such as\nstring, in a compact space so that metadata can then be simply stored in an\narray. While it is known that just 1.44 bits per key are necessary to store a\nminimal perfect function, no published technique can go below 2 bits per key\nin practice. We propose a new technique for storing minimal perfect hash\nfunctions with expected linear construction time and expected constant lookup\ntime that makes it possible to build for the first time, for example,\nstructures which need 1.56 bits per key, that is, within 8.3\nbound, in less than 2 ms per key. We show that instances of our construction\nare able to simultaneously beat the construction time, space usage and lookup\ntime of the state-of-the-art data structure reaching 2 bits per key.\nMoreover, we provide parameter choices giving structures which are competitive\nwith alternative, larger-size data structures in terms of space and lookup\ntime. The construction of our data structures can be easily parallelized or\nmapped on distributed computational units (e.g., within the MapReduce\nframework), and structures larger than the available RAM can be directly built\nin mass storage."
<http://api.deepai.org/profile/sebastiano-vigna>