hashtable

I want to implement a HashTable (or mabybe a HashSet or Dictionary ) which has unique members which expire after a while. For example: // Items expire automatically after 10 seconds (Expiration period = 10 sec) bool result = false; // Starting from second 0 result = MyHashSet.Add("Bob"); // second 0 => true result = MyHashSet.Add("Alice"); // second 5 => true result = MyHashSet.Add("Bob"); // second 8 => false (item already exist) result = MyHashSet.Add("Bob"); // second 12 => true (Bob has expired) How to do that in a thread-safe manner with lowest costs? You could create you own Hash Table

I have heard that, for example, MurmurHash2 is not "incremental" but MurmurHash3 is incremental. What does this mean? And why is it useful? Incremental hash functions suited for situations where if a previously hashed message, M is slightly updated into a new message, M*, then it should be fairly quick to compute the hash value of the updated message, M*. This is done by computing the new hash, m*, from the old hash value, m, in contrast to conventional hash functions that have to recompute the new hash, m* from scratch, which takes a longer time. http://www.cs.berkeley.edu/~daw/papers/inchash

What is size of a hash table with 32 bit key and 32 bit pointers to values stored separately? Is it going to be 2^32 slots * (4 Bytes (key) + 4 Bytes (pointers to values)) = 4 * 10^9 * (4 + 4) = 32GB ? I am trying to understand space complexity of hash tables. DigitalRoss Hash tables don't match hash function values and slots. The hash function is computed modulo the size of a reference vector that is much smaller than the hash function range. Because this value is fixed, it is not considered in the space complexity computation. Consequently, the space complexity of every reasonable hash table

According to the HashSet javadoc, HashSet.contains only returns a boolean. How can I "find" an object in a hashSet and modify it (it's not a primitive data type)? I see that HashTable has a get() method, but I would prefer to use the set. You can remove an element and add a different one. Modifying an object while it is in a hash set is a recipe for disaster (if the modification changes the hash value or equality behavior). To quote the source of the stock Sun java.util.HashSet: public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, java.io.Serializable { static final

I need to implement a structure in Java that is a key-value list (of types Integer-String) and I want to shuffle it. Basically, I would like to do something like that. public LinkedHashMap<Integer, String> getQuestionOptionsMap(){ LinkedHashMap<Integer, String> shuffle = new LinkedHashMap<Integer, String> (); if (answer1 != null) shuffle.put(new Integer(1), answer1); if (answer2 != null) shuffle.put(new Integer(2), answer2); if (answer3 != null) shuffle.put(new Integer(3), answer3); if (answer4 != null) shuffle.put(new Integer(4), answer4); Collections.shuffle(shuffle); return shuffle; }

I was looking up the difference between the two classes and this point came up in a lot of the answers with this blog being the source: http://javarevisited.blogspot.com/2010/10/difference-between-hashmap-and.html However I don't completely get it. Can someone elaborate this? Perhaps with an example? Thanks for looking in! evanwong Fail-fast means when you try to modify the content when you are iterating thru it, it will fail and throw ConcurrentModificationException. Set keys = hashMap.keySet(); for (Object key : keys) { hashMap.put(someObject, someValue); //it will throw the

Is there a way to map a list onto a dictionary? What I want to do is give it a function that will return the name of a key, and the value will be the original value. For example; somefunction(lambda a: a[0], ["hello", "world"]) => {"h":"hello", "w":"world"} (This isn't a specific example that I want to do, I want a generic function like map() that can do this) I don't think a standard function exists that does exactly that, but it's very easy to construct one using the dict builtin and a comprehension: def somefunction(keyFunction, values): return dict((keyFunction(v), v) for v in values)