For C++, a map works well. Several million objects won’t be a problem. 10 million items took about 4.4 seconds and about 57 meg on my computer. My test application is as follows: #include <stdio.h> #include <stdlib.h> #include <map> class triple { public: int x; int y; int z; bool operator<(const triple &other) const { … Read more
Which method has less collisions, is faster and easier to read? TLDR The random_choice is the fastest, has fewer collisions but is IMO slightly harder to read. The most readable is shortuuid_random but is an external dependency and is slightly slower and has 6x the collisions. The methods alphabet = string.ascii_lowercase + string.digits su = … Read more
Use Hash’s values_at method: from, to, name = hash.values_at(:from, :to, :name) This will return nil for any keys that don’t exist in the hash.
Here’s a straight forward implementation of the md5sum command that computes and displays the MD5 of the file specified on the command-line. It needs to be linked against the OpenSSL library (gcc md5.c -o md5 -lssl) to work. It’s pure C, but you should be able to adapt it to your C++ application easily enough. … Read more
__hash__ should return the same value for objects that are equal. It also shouldn’t change over the lifetime of the object; generally you only implement it for immutable objects. A trivial implementation would be to just return 0. This is always correct, but performs badly. Your solution, returning the hash of a tuple of properties, … Read more
hash[:new_key] = hash.delete :old_key
Take a look at the 128-bit variant of MurmurHash3. The algorithm’s page includes some performance numbers. Should be possible to port this to Python, pure or as a C extension. (Updated the author recommends using the 128-bit variant and throwing away the bits you don’t need). If MurmurHash2 64-bit works for you, there is a … Read more
The syntax is for defining Hash key/value pairs, and the difference depends on the Ruby version. Supported in both Ruby 1.8 and Ruby 1.9 :foo => true Supported only in Ruby 1.9 foo: true If you’re developing in Ruby 1.9 you should probably use the syntax: foo: true as it appears to be the direction … Read more
The map has to work out which internal table index to use for any given key, mapping any int value (could be negative) to a value in the range [0, table.length). When table.length is a power of two, that can be done really cheaply – and is, in indexFor: static int indexFor(int h, int length) … Read more
The correct answer from a theoretical point of view is: Use std::hash which is likely specialized to be as good as it gets, and if that is not applicable, use a good hash function rather than a fast one. The speed of the hash function does not matter so much as its quality. The practical … Read more