They are entirely different constructs. A HashMap is an implementation of Map. A Map maps keys to values. The key look up occurs using the hash. On the other hand, a HashSet is an implementation of Set. A Set is designed to match the mathematical model of a set. A HashSet does use a HashMap to back its implementation, as you noted. However, it implements an entirely different interface. … Read more
Your algorithm is fine. However int is too small for your computations, it fails for this input: At some point integer overflows to negative value and your implementation goes crazy, recursing infinitely. Change int num to long num and you’ll be fine – for some time. Later you’ll need BigInteger. Note that according to Wikipedia on Collatz conjecture (bold mine): The longest progression for … Read more
Hash your objects yourself manually, and use the resulting strings as keys for a regular JavaScript dictionary. After all, you are in the best position to know what makes your objects unique. That’s what I do. Example: This way you can control indexing done by JavaScript without heavy lifting of memory allocation, and overflow handling. … Read more
Yes, it is a hash mapping or hash table. You can read a description of python’s dict implementation, as written by Tim Peters, here. That’s why you can’t use something ‘not hashable’ as a dict key, like a list: You can read more about hash tables or check how it has been implemented in python and why it is implemented that … Read more
Python dictionary is a built-in type that supports key-value pairs. as well as using the dict keyword: or:
The standard library includes the ordered and the unordered map (std::map and std::unordered_map) containers. In an ordered map the elements are sorted by the key, insert and access is in O(log n). Usually the standard library internally uses red black trees for ordered maps. But this is just an implementation detail. In an unordered map insert and access is in … Read more
The standard library includes the ordered and the unordered map (std::map and std::unordered_map) containers. In an ordered map the elements are sorted by the key, insert and access is in O(log n). Usually the standard library internally uses red black trees for ordered maps. But this is just an implementation detail. In an unordered map insert and access is in … Read more
There are several differences between HashMap and Hashtable in Java: Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values. One of HashMap’s subclasses is LinkedHashMap, so in the event that you’d want predictable iteration order (which is insertion order by default), you … Read more