I think what you’re looking for is not directly possible. One important property of equality is that it is transitive. (ie. If a == b and b == c, then a == c). With a distance measure, though, you really don’t want this property. Example: Take a single float (for simplicity). Suppose we want to … Read more
The following article addresses this question in some detail: HashMap requires a better hashCode() – JDK 1.4 Part II. According to that article, the main reason to move to power-of-two sizes was that bit masking is faster than integer division. This is not without adverse consequences, which are explained by one of the original authors: … Read more
You can see the implementation of hashCode function in java.util.ArrayList as public int hashCode() { int hashCode = 1; Iterator<E> i = iterator(); while (i.hasNext()) { E obj = i.next(); hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode()); } return hashCode; } It is one such example and your Eclipse generated code follows a … Read more
Most compilers should define std::hash_map for you; in the coming C++0x standard, it will be part of the standard library as std::unordered_map. The STL Page on it is fairly standard. If you use Visual Studio, Microsoft has a page on it. If you want to use your class as the value, not as the key, … Read more
A bucket is simply a fast-access location (like an array index) that is the the result of the hash function. The idea with hashing is to turn a complex input value into a different value which can be used to rapidly extract or store data. Consider the following hash function for mapping people’s names into … Read more
Because: 0x7FFFFFFF is 0111 1111 1111 1111 1111 1111 1111 1111 : all 1 except the sign bit. (hash & 0x7FFFFFFF) will result in a positive integer. (hash & 0x7FFFFFFF) % tab.length will be in the range of the tab length.
Now assumming you want a hash, and want something blazing fast that would work in your case, because your strings are just 6 chars long you could use this magic: size_t precision = 2; //change the precision with this size_t hash(const char* str) { return (*(size_t*)str)>> precision; } CRC is for slowpokes 😉 Explanation: This … Read more
I’m surprised that you saw chained hashing to be faster than linear probing – in practice, linear probing is typically significantly faster than chaining. This is primarily due to locality of reference, since the accesses performed in linear probing tend to be closer in memory than the accesses performed in chained hashing. There are other … Read more
You can’t do what you’re trying to do: bash arrays are one-dimensional $ declare -A PERSONS $ declare -A PERSON $ PERSON[“FNAME”]=’John’ $ PERSON[“LNAME”]=’Andrew’ $ declare -p PERSON declare -A PERSON='([FNAME]=”John” [LNAME]=”Andrew” )’ $ PERSONS[1]=([FNAME]=”John” [LNAME]=”Andrew” ) bash: PERSONS[1]: cannot assign list to array member You can fake multidimensionality by composing a suitable array index … Read more
In Computing Science terminology, a map is an associative container mapping from a key to a value. In other words, you can do operations like “for key K remember value V” and later “for key K get the value”. A map can be implemented in many ways – for example, with a (optionally balanced) binary … Read more