I read in the specifications for graphs implemented with Adjacency List that adding edges is done in constant time. BUT that would require a node lookup with O(1). I would like best possible performance. The question here is which datatype would would give me that. Hashmap has been considered, worst case with hashmap is still O(n). Cou...
public interface InnerMap<V> extends Map<String, V> { Map<String, V> getInnerMap(String prefix); } For example: baseMap.put("aabb", "one"); baseMap.put("aabbddd", "two"); InnerMap map1 = baseMap.getInnerMap("aa"); map1.get("bb") => "one" map1.get("bbdd") => "two" map1.get("aa") => null map2 = map1.getInnerMap("bb"); map2.get("dd")...
I have been trying to understand the internal implementation of java.util.HashMap and java.util.HashSet. Following are the doubts popping in my mind for a while: Whats is the importance of the @Override public int hashcode() in a HashMap/HashSet? Where is this hash code used internally? I have generally seen the key of the HashMap be ...
In Python, the defaultdict class provides a convenient way to create a mapping from key -> [list of values], in the following example, from collections import defaultdict d = defaultdict(list) d[1].append(2) d[1].append(3) # d is now {1: [2, 3]} Is there an equivalent to this in Java? Why I chose Tendayi Mawushe's solution This solu...
I have a HashMap with various keys and values, how can I get one value out? I have a key in the map called my_code, it should contain a string, how can I just get that without having to iterate through the map? So far I've got.. HashMap newMap = new HashMap(paramMap); String s = newMap.get("my_code").toString(); I'm expecting ...
The hash structures I am aware of - HashTable, HashSet & HashMap. Do they all use the bucket structure - ie when two hashcodes are similar exactly the same one element does not overwrite the other, instead they are placed in the same bucket associated with that hashcode? ...
Hey everyone, Is there any reason that I would be missing the java.util.HashMap package? I have java.util.Hashtable, but no HashMap... I have the most up to date JDK and JRE... Thanks! ...
What is the most efficient way to count all the different keys in a hash_multimap? E.g. if I have a already filled hash_multimap, (e.g. a container where you can store multiple entities with a same key) how can i retrieve the set of keys? ...
I have a pair I know the value of the pair.first cannot be more than 1000. I also know that the pair.second , the string, is always 1 word. Never more than 1 word. So, to construct the Hash value for the pair I am doing the following: pair<int,string> p; hash<char*> H; hash_vale = H(p.second)*1000 + p.first; I think this will give uni...
I'm writing a Java program that parses all the words from a text file and then adds them to a HashMap. I need to count how many distinct words are contained in the file. I also need to figure out the highest counted words. The HashMap is comprised of each word mapped to an integer which represents how many times the word occurs. Is the...
I'm using Boost's implementation of a hash map in a project right now, and I'm trying to implement a custom type for keys. I have four unsigned integers which I'd like to combine into a single 128-bit datatype to use as a key. I've created a struct with a 32-bit integer array of four elements, which serves as my storage. To be honest, I...
Hello, the related Questions couldn't help me very much. How can i loop through a HashMap in jsp like this example: <% HashMap<String, String> countries = MainUtils.getCountries(l); %> <select name="ccountry" id="ccountry" > <% //HERE I NEED THE LOOP %> </select>*<br/> ...
I have a requirement to create a java cache which holds all the cities and airports. So, if i query the cache for a location, lets say a city, it should return all the airports in that city and if I query a location which is an airport, i should get back that airport. Also, each location has to be stored as a byte array in cache.(as the...
I have a List of Foo Objects. If a name appears multiple times, I want to do something to the first Item with that name. HashMap<String, Foo> map = new HashMap<String, Foo>(); for (Foo bar: this.FooList) { if (!map.containsKey(bar.getName())) { map.put(bar.getName(), bar); } else { map.get(bar.getName...
Here is my use case, I have an object that is logically equal to my HashMap key but not the same object (not ==). I need to get the actuall key object out of the HashMap so that i can synchronise on it. I am aware that i can iterate over the ketSet, but this is slow in comparison to hashing. Looking through the java.util.HashMap impleme...
I'm using this method to move from a state to the next on this automaton simulator: public void processString (String string){ StringBuilder stepString= new StringBuilder (string); int actualStateIntIndex; System.out.println("THE FOUND INITIAL ONE IS "+ theInitialStateIntIndex); State firstState = allStates.get(theInitial...
I want to put State objects (which are HashMaps with Character as key and State as Value into an ArrayList named allStates. Should I override the equals and hashCode methods here? Why? How? This code is for the Automaton and State classes I've built so far: class State extends HashMap<Character, State>{ boolean isFinal; boolean isIni...
Hi, I have an application which displays a collection of objects in rows, one object = one row. The objects are stored in a HashMap. The order of the rows does not affect the functionality of the application (that is why a HashMap was used instead of a sortable collection). However I have noticed that the same aplication runs different...
I understand that the Set returned from a Map's keySet() method does not guarantee any particular order. My question is, does it guarantee the same order over multiple iterations. For example Map<K,V> map = getMap(); for( K k : map.keySet() ) { } ... for( K k : map.keySet() ) { } In the above code, assuming that the map is not mo...
About the 8 Puzzle Problem // Breadth First Search Usage in the common Eight Puzzle Problem. import java.util.*; class EightPuzzle { Queue<String> q = new LinkedList<String>(); // Use of Queue Implemented using LinkedList for Storing All the Nodes in BFS. Map<String,Integer> map = new HashMap<String, Integer>(); // HashMap...