A hash table is a data structure used to implement an associative array (a structure that can map keys to values). It uses a "hash function" to compute an index into an array from which the value can be found.
Hash tables (wikipedia) are part of the standard libraries for many languages:
- C# and other .net languages:
ConcurrentHashMap, and others (including the rather aged
- Python: "Dictionary"
it is a relatively common exercise in computer science courses to reimplement a hash table from first principles.