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Change project structure to a Maven Java project + Refactor (#2816)
This commit is contained in:
Aitor Fidalgo Sánchez
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9fb3364ccc
@ -0,0 +1,183 @@
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package com.thealgorithms.datastructures.caches;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* Least recently used (LRU)
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* <p>
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* Discards the least recently used items first. This algorithm requires keeping
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* track of what was used when, which is expensive if one wants to make sure the
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* algorithm always discards the least recently used item.
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* https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)
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*
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* @param <K> key type
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* @param <V> value type
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*/
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public class LRUCache<K, V> {
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private final Map<K, Entry<K, V>> data = new HashMap<>();
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private Entry<K, V> head;
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private Entry<K, V> tail;
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private int cap;
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private static final int DEFAULT_CAP = 100;
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public LRUCache() {
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setCapacity(DEFAULT_CAP);
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}
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public LRUCache(int cap) {
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setCapacity(cap);
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}
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private void setCapacity(int newCapacity) {
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checkCapacity(newCapacity);
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for (int i = data.size(); i > newCapacity; i--) {
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Entry<K, V> evicted = evict();
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data.remove(evicted.getKey());
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}
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this.cap = newCapacity;
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}
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private Entry<K, V> evict() {
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if (head == null) {
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throw new RuntimeException("cache cannot be empty!");
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}
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Entry<K, V> evicted = head;
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head = evicted.getNextEntry();
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head.setPreEntry(null);
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evicted.setNextEntry(null);
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return evicted;
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}
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private void checkCapacity(int capacity) {
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if (capacity <= 0) {
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throw new RuntimeException("capacity must greater than 0!");
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}
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}
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public V get(K key) {
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if (!data.containsKey(key)) {
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return null;
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}
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final Entry<K, V> entry = data.get(key);
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moveNodeToLast(entry);
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return entry.getValue();
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}
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private void moveNodeToLast(Entry<K, V> entry) {
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if (tail == entry) {
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return;
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}
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final Entry<K, V> preEntry = entry.getPreEntry();
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final Entry<K, V> nextEntry = entry.getNextEntry();
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if (preEntry != null) {
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preEntry.setNextEntry(nextEntry);
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}
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if (nextEntry != null) {
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nextEntry.setPreEntry(preEntry);
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}
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if (head == entry) {
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head = nextEntry;
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}
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tail.setNextEntry(entry);
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entry.setPreEntry(tail);
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entry.setNextEntry(null);
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tail = entry;
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}
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public void put(K key, V value) {
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if (data.containsKey(key)) {
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final Entry<K, V> existingEntry = data.get(key);
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existingEntry.setValue(value);
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moveNodeToLast(existingEntry);
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return;
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}
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Entry<K, V> newEntry;
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if (data.size() == cap) {
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newEntry = evict();
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data.remove(newEntry.getKey());
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} else {
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newEntry = new Entry<>();
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}
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newEntry.setKey(key);
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newEntry.setValue(value);
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addNewEntry(newEntry);
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data.put(key, newEntry);
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}
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private void addNewEntry(Entry<K, V> newEntry) {
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if (data.isEmpty()) {
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head = newEntry;
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tail = newEntry;
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return;
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}
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tail.setNextEntry(newEntry);
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newEntry.setPreEntry(tail);
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newEntry.setNextEntry(null);
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tail = newEntry;
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}
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static final class Entry<I, J> {
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private Entry<I, J> preEntry;
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private Entry<I, J> nextEntry;
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private I key;
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private J value;
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public Entry() {
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}
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public Entry(Entry<I, J> preEntry, Entry<I, J> nextEntry, I key, J value) {
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this.preEntry = preEntry;
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this.nextEntry = nextEntry;
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this.key = key;
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this.value = value;
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}
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public Entry<I, J> getPreEntry() {
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return preEntry;
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}
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public void setPreEntry(Entry<I, J> preEntry) {
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this.preEntry = preEntry;
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}
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public Entry<I, J> getNextEntry() {
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return nextEntry;
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}
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public void setNextEntry(Entry<I, J> nextEntry) {
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this.nextEntry = nextEntry;
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}
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public I getKey() {
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return key;
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}
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public void setKey(I key) {
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this.key = key;
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}
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public J getValue() {
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return value;
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}
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public void setValue(J value) {
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this.value = value;
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}
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}
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public static void main(String[] args) {
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final LRUCache<String, Integer> cache = new LRUCache<>(2);
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cache.put("Key1", 1);
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cache.put("Key2", 2);
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cache.put("Key3", 3);
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cache.put("Key4", 4);
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System.out.println("getValue(Key1): " + cache.get("Key1"));
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System.out.println("getValue(Key2): " + cache.get("Key2"));
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System.out.println("getValue(Key3): " + cache.get("Key3"));
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System.out.println("getValue(Key4): " + cache.get("Key4"));
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}
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}
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@ -0,0 +1,181 @@
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package com.thealgorithms.datastructures.caches;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* Most recently used (MRU)
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* <p>
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* In contrast to Least Recently Used (LRU), MRU discards the most recently used
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* items first.
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* https://en.wikipedia.org/wiki/Cache_replacement_policies#Most_recently_used_(MRU)
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*
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* @param <K> key type
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* @param <V> value type
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*/
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public class MRUCache<K, V> {
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private final Map<K, Entry<K, V>> data = new HashMap<>();
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private Entry<K, V> head;
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private Entry<K, V> tail;
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private int cap;
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private static final int DEFAULT_CAP = 100;
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public MRUCache() {
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setCapacity(DEFAULT_CAP);
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}
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private void setCapacity(int newCapacity) {
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checkCapacity(newCapacity);
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for (int i = data.size(); i > newCapacity; i--) {
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Entry<K, V> evicted = evict();
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data.remove(evicted.getKey());
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}
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this.cap = newCapacity;
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}
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private void checkCapacity(int capacity) {
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if (capacity <= 0) {
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throw new RuntimeException("capacity must greater than 0!");
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}
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}
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private Entry<K, V> evict() {
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if (head == null) {
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throw new RuntimeException("cache cannot be empty!");
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}
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final Entry<K, V> evicted = this.tail;
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tail = evicted.getPreEntry();
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tail.setNextEntry(null);
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evicted.setNextEntry(null);
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return evicted;
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}
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public MRUCache(int cap) {
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setCapacity(cap);
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}
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public V get(K key) {
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if (!data.containsKey(key)) {
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return null;
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}
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final Entry<K, V> entry = data.get(key);
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moveEntryToLast(entry);
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return entry.getValue();
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}
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public void put(K key, V value) {
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if (data.containsKey(key)) {
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final Entry<K, V> exitingEntry = data.get(key);
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exitingEntry.setValue(value);
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moveEntryToLast(exitingEntry);
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return;
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}
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Entry<K, V> newEntry;
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if (data.size() == cap) {
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newEntry = evict();
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data.remove(newEntry.getKey());
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} else {
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newEntry = new Entry<>();
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}
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newEntry.setKey(key);
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newEntry.setValue(value);
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addNewEntry(newEntry);
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data.put(key, newEntry);
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}
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private void addNewEntry(Entry<K, V> newEntry) {
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if (data.isEmpty()) {
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head = newEntry;
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tail = newEntry;
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return;
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}
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tail.setNextEntry(newEntry);
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newEntry.setPreEntry(tail);
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newEntry.setNextEntry(null);
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tail = newEntry;
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}
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private void moveEntryToLast(Entry<K, V> entry) {
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if (tail == entry) {
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return;
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}
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final Entry<K, V> preEntry = entry.getPreEntry();
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final Entry<K, V> nextEntry = entry.getNextEntry();
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if (preEntry != null) {
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preEntry.setNextEntry(nextEntry);
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}
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if (nextEntry != null) {
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nextEntry.setPreEntry(preEntry);
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}
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if (head == entry) {
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head = nextEntry;
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}
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tail.setNextEntry(entry);
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entry.setPreEntry(tail);
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entry.setNextEntry(null);
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tail = entry;
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}
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static final class Entry<I, J> {
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private Entry<I, J> preEntry;
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private Entry<I, J> nextEntry;
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private I key;
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private J value;
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public Entry() {
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}
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public Entry(Entry<I, J> preEntry, Entry<I, J> nextEntry, I key, J value) {
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this.preEntry = preEntry;
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this.nextEntry = nextEntry;
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this.key = key;
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this.value = value;
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}
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public Entry<I, J> getPreEntry() {
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return preEntry;
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}
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public void setPreEntry(Entry<I, J> preEntry) {
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this.preEntry = preEntry;
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}
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public Entry<I, J> getNextEntry() {
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return nextEntry;
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}
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public void setNextEntry(Entry<I, J> nextEntry) {
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this.nextEntry = nextEntry;
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}
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public I getKey() {
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return key;
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}
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public void setKey(I key) {
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this.key = key;
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}
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public J getValue() {
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return value;
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}
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public void setValue(J value) {
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this.value = value;
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}
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}
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public static void main(String[] args) {
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final MRUCache<String, Integer> cache = new MRUCache<>(2);
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cache.put("Key1", 1);
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cache.put("Key2", 2);
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cache.put("Key3", 3);
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cache.put("Key4", 4);
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System.out.println("getValue(Key1): " + cache.get("Key1"));
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System.out.println("getValue(Key2): " + cache.get("Key2"));
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System.out.println("getValue(Key3): " + cache.get("Key3"));
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System.out.println("getValue(Key4): " + cache.get("Key4"));
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}
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}
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