leetcode/LRUCache.java at master · Susheng/leetcode · GitHub

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importjava.util.HashMap;
importjava.util.Map;

/**
 * Design and implement a data structure for Least Recently Used (LRU) cache. It
 * should support the following operations: get and set.
 *
 * get(key) - Get the value (will always be positive) of the key if the key
 * exists in the cache, otherwise return -1. set(key, value) - Set or insert the
 * value if the key is not already present. When the cache reached its capacity,
 * it should invalidate the least recently used item before inserting a new
 * item.
 *
 */

publicclassLRUCache {

publicclassCacheItem<K, V> {

privateKkey;
privateVvalue;
privateCacheItem<K, V> prev;
privateCacheItem<K, V> next;

publicCacheItem<K, V> getPrev() {
returnprev;
 }

publicvoidsetPrev(CacheItem<K, V> prev) {
this.prev = prev;
 }

publicCacheItem<K, V> getNext() {
returnnext;
 }

publicvoidsetNext(CacheItem<K, V> next) {
this.next = next;
 }

publicCacheItem(Kkey, Vvalue) {
this.key = key;
this.value = value;
 }
	}

publicclassBidirectionalList<K, V> {
privateCacheItem<K, V> head = newCacheItem<K, V>(null, null);
privateCacheItem<K, V> tail = head;

publicvoidinsertTail(CacheItem<K, V> node) {
tail.next = node;
node.prev = tail;
node.next = null;
tail = node;
 }

publicvoiddelete(CacheItem<K, V> node) {
if (head.next == null)
return;
if (node == head.next) {
deleteHead();
 } elseif (node == tail) {
deleteTail();
 } else {
node.prev.next = node.next;
node.next.prev = node.prev;
node.next = null;
node.prev = null;
 }
 }

publicCacheItem<K, V> deleteTail() {
if (head.next == null)
returnnull;
CacheItem<K, V> ret = tail;
tail = tail.prev;
tail.next = null;
ret.prev = null;
ret.next = null;
returnret;
 }

publicCacheItem<K, V> deleteHead() {
if (head.next == null)
returnnull;
if (head.next == tail) {
tail = tail.prev;
 }
CacheItem<K, V> ret = head.next;
head.next = ret.next;
if (ret.next != null) {
ret.next.prev = head;
 }
ret.next = null;
ret.prev = null;
returnret;
 }
	}

privateMap<Integer, CacheItem<Integer, Integer>> cacheMap = newHashMap<Integer, CacheItem<Integer, Integer>>();
privateBidirectionalList<Integer, Integer> cacheList = newBidirectionalList<Integer, Integer>();
privateintcacheSize = 0;
privateintcapacity;

publicLRUCache(intcapacity) {
this.capacity = capacity;
	}

publicintget(intkey) {
CacheItem<Integer, Integer> itm = cacheMap.get(key);
if (itm == null)
return -1;
cacheList.delete(itm);
cacheList.insertTail(itm);
returnitm.value.intValue();
	}

publicvoidset(intkey, intvalue) {
if (cacheMap.containsKey(key)) {
updateItem(key, value);
 } elseif (cacheSize == capacity && removeLeastUsed()) {
cacheSize--;
addItem(key, value);
 } else {
addItem(key, value);
 }
	}

privatevoidaddItem(intkey, intvalue) {
CacheItem<Integer, Integer> newCacheItem = newCacheItem<Integer, Integer>(
key, value);
cacheList.insertTail(newCacheItem);
cacheMap.put(key, newCacheItem);
cacheSize++;
	}

privatevoidupdateItem(intkey, intvalue) {
CacheItem<Integer, Integer> exitedKey = cacheMap.get(key);
exitedKey.value = value;
cacheList.delete(exitedKey);
cacheList.insertTail(exitedKey);
	}

privatebooleanremoveLeastUsed() {
CacheItem<Integer, Integer> removedKey = cacheList.deleteHead();
cacheMap.remove(removedKey.key);
returnremovedKey == null ? false : true;
	}
}