Add MRU Cache (#2738)
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januslinhc
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@ -3,6 +3,7 @@
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* [IIRFilter](https://github.com/TheAlgorithms/Java/blob/master/AudioFilters/IIRFilter.java)
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## Backtracking
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* [KnightsTour](https://github.com/TheAlgorithms/Java/blob/master/Backtracking/KnightsTour.java)
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* [NQueens](https://github.com/TheAlgorithms/Java/blob/master/Backtracking/NQueens.java)
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* [PowerSum](https://github.com/TheAlgorithms/Java/blob/master/Backtracking/PowerSum.java)
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@ -48,6 +49,7 @@
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* [CircularBuffer](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Buffers/CircularBuffer.java)
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* Caches
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* [LRUCache](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Caches/LRUCache.java)
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* [MRUCache](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Caches/MRUCache.java)
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* DisjointSets
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* [DisjointSets](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/DisjointSets/DisjointSets.java)
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* [Node](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/DisjointSets/Node.java)
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@ -82,6 +84,7 @@
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* Lists
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* [CircleLinkedList](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Lists/CircleLinkedList.java)
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* [CountSinglyLinkedListRecursion](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Lists/CountSinglyLinkedListRecursion.java)
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* [CreateAndDetectLoop](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Lists/CreateAndDetectLoop.java)
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* [CursorLinkedList](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Lists/CursorLinkedList.java)
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* [DoublyLinkedList](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Lists/DoublyLinkedList.java)
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* [Merge K SortedLinkedlist](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Lists/Merge_K_SortedLinkedlist.java)
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@ -113,11 +116,14 @@
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* [BSTRecursive](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/BSTRecursive.java)
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* [BSTRecursiveGeneric](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/BSTRecursiveGeneric.java)
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* [CeilInBinarySearchTree](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/CeilInBinarySearchTree.java)
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* [CreateBinaryTreeFromInorderPreorder](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/CreateBinaryTreeFromInorderPreorder.java)
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* [CreateBSTFromSortedArray](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/CreateBSTFromSortedArray.java)
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* [FenwickTree](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/FenwickTree.java)
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* [GenericTree](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/GenericTree.java)
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* [LCA](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/LCA.java)
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* [LevelOrderTraversal](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/LevelOrderTraversal.java)
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* [LevelOrderTraversalQueue](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/LevelOrderTraversalQueue.java)
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* [nearestRightKey](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/nearestRightKey.java)
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* [PrintTopViewofTree](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/PrintTopViewofTree.java)
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* [RedBlackBST](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/RedBlackBST.java)
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* [SegmentTree](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Trees/SegmentTree.java)
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@ -253,6 +259,7 @@
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## Others
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* [BestFit](https://github.com/TheAlgorithms/Java/blob/master/Others/BestFit.java)
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* [BFPRT](https://github.com/TheAlgorithms/Java/blob/master/Others/BFPRT.java)
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* [BoyerMoore](https://github.com/TheAlgorithms/Java/blob/master/Others/BoyerMoore.java)
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* [BrianKernighanAlgorithm](https://github.com/TheAlgorithms/Java/blob/master/Others/BrianKernighanAlgorithm.java)
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* [CountChar](https://github.com/TheAlgorithms/Java/blob/master/Others/CountChar.java)
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* [CountWords](https://github.com/TheAlgorithms/Java/blob/master/Others/CountWords.java)
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@ -317,6 +324,7 @@
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* [SquareRootBinarySearch](https://github.com/TheAlgorithms/Java/blob/master/Searches/SquareRootBinarySearch.java)
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* [TernarySearch](https://github.com/TheAlgorithms/Java/blob/master/Searches/TernarySearch.java)
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* [UnionFind](https://github.com/TheAlgorithms/Java/blob/master/Searches/UnionFind.java)
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* [UpperBound](https://github.com/TheAlgorithms/Java/blob/master/Searches/UpperBound.java)
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## Sorts
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* [BitonicSort](https://github.com/TheAlgorithms/Java/blob/master/Sorts/BitonicSort.java)
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179
DataStructures/Caches/MRUCache.java
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179
DataStructures/Caches/MRUCache.java
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package 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 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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