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For example, one could define a dictionary having a string "toast" mapped to the integer 42 or vice versa. The keys in a dictionary must be of an immutable Python type, such as an integer or a string, because under the hood they are implemented via a hash function. This makes for much faster lookup times, but requires keys not change.
In computer science, a hash table is a data structure that implements an associative array, also called a dictionary or simply map; an associative array is an abstract data type that maps keys to values. [2] A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired ...
An invocation of gethash actually returns two values: the value or substitute value for the key and a boolean indicator, returning T if the hash table contains the key and NIL to signal its absence. ( multiple-value-bind ( value contains-key ) ( gethash "Sally Smart" phone-book ) ( if contains-key ( format T "~&The associated value is: ~s ...
Any existing mapping is overwritten. The arguments to this operation are the key and the value. Remove or delete remove a (,) pair from the collection, unmapping a given key from its value. The argument to this operation is the key. Lookup, find, or get find the value (if any) that is bound to a given key.
The same technique can be used to map two-letter country codes like "us" or "za" to country names (26 2 = 676 table entries), 5-digit ZIP codes like 13083 to city names (100 000 entries), etc. Invalid data values (such as the country code "xx" or the ZIP code 00000) may be left undefined in the table or mapped to some appropriate "null" value.
For example, key k could be the node ID and associated data could describe how to contact this node. This allows publication-of-presence information and often used in IM applications, etc. In the simplest case, ID is just a random number that is directly used as key k (so in a 160-bit DHT ID will be a 160-bit number, usually randomly chosen ...
The symbol table must have some means of differentiating references to the different "p"s. A common data structure used to implement symbol tables is the hash table . The time for searching in hash tables is independent of the number of elements stored in the table, so it is efficient for a large number of elements.
Trie-Find(x, key) for 0 ≤ i < key.length do if x.Children[key[i]] = nil then return false end if x := x.Children[key[i]] repeat return x.Value In the above pseudocode, x and key correspond to the pointer of trie's root node and the string key respectively.