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| public class LFUCache {
private final Map cache;
private final LinkedHashSet[] frequencyList;
private int lowestFrequency;
private int maxFrequency;
private final int maxCacheSize;
// @param capacity, an integer
public LFUCache(int capacity) {
// Write your code here
this.cache = new HashMap(capacity);
this.frequencyList = new LinkedHashSet[capacity * 2];
this.lowestFrequency = 0;
this.maxFrequency = capacity * 2 - 1;
this.maxCacheSize = capacity;
initFrequencyList();
}
// @param key, an integer
// @param value, an integer
// @return nothing
public void set(int key, int value) {
// Write your code here
CacheNode currentNode = cache.get(key);
if (currentNode == null) {
if (cache.size() == maxCacheSize) {
doEviction();
}
LinkedHashSet nodes = frequencyList[0];
currentNode = new CacheNode(key, value, 0);
nodes.add(currentNode);
cache.put(key, currentNode);
lowestFrequency = 0;
} else {
currentNode.v = value;
}
addFrequency(currentNode);
}
public int get(int key) {
// Write your code here
CacheNode currentNode = cache.get(key);
if (currentNode != null) {
addFrequency(currentNode);
return currentNode.v;
} else {
return -1;
}
}
public void addFrequency(CacheNode currentNode) {
int currentFrequency = currentNode.frequency;
if (currentFrequency
int nextFrequency = currentFrequency + 1;
LinkedHashSet currentNodes = frequencyList[currentFrequency];
LinkedHashSet newNodes = frequencyList[nextFrequency];
moveToNextFrequency(currentNode, nextFrequency, currentNodes, newNodes);
cache.put(currentNode.k, currentNode);
if (lowestFrequency == currentFrequency && currentNodes.isEmpty()) {
lowestFrequency = nextFrequency;
}
} else {
// Hybrid with LRU: put most recently accessed ahead of others:
LinkedHashSet nodes = frequencyList[currentFrequency];
nodes.remove(currentNode);
nodes.add(currentNode);
}
}
public int remove(int key) {
CacheNode currentNode = cache.remove(key);
if (currentNode != null) {
LinkedHashSet nodes = frequencyList[currentNode.frequency];
nodes.remove(currentNode);
if (lowestFrequency == currentNode.frequency) {
findNextLowestFrequency();
}
return currentNode.v;
} else {
return -1;
}
}
public int frequencyOf(int key) {
CacheNode node = cache.get(key);
if (node != null) {
return node.frequency + 1;
} else {
return 0;
}
}
public void clear() {
for (int i = 0; i <= maxFrequency; i++) {
frequencyList[i].clear();
}
cache.clear();
lowestFrequency = 0;
}
public int size() {
return cache.size();
}
public boolean isEmpty() {
return this.cache.isEmpty();
}
public boolean containsKey(int key) {
return this.cache.containsKey(key);
}
private void initFrequencyList() {
for (int i = 0; i <= maxFrequency; i++) {
frequencyList[i] = new LinkedHashSet();
}
}
private void doEviction() {
int currentlyDeleted = 0;
double target = 1; // just one
while (currentlyDeleted
LinkedHashSet nodes = frequencyList[lowestFrequency];
if (nodes.isEmpty()) {
break;
} else {
Iterator it = nodes.iterator();
while (it.hasNext() && currentlyDeleted++
CacheNode node = it.next();
it.remove();
cache.remove(node.k);
}
if (!it.hasNext()) {
findNextLowestFrequency();
}
}
}
}
private void moveToNextFrequency(CacheNode currentNode, int nextFrequency,
LinkedHashSet currentNodes,
LinkedHashSet newNodes) {
currentNodes.remove(currentNode);
newNodes.add(currentNode);
currentNode.frequency = nextFrequency;
}
private void findNextLowestFrequency() {
while (lowestFrequency <= maxFrequency && frequencyList[lowestFrequency].isEmpty()) {
lowestFrequency++;
}
if (lowestFrequency > maxFrequency) {
lowestFrequency = 0;
}
}
private class CacheNode {
public final int k;
public int v;
public int frequency;
public CacheNode(int k, int v, int frequency) {
this.k = k;
this.v = v;
this.frequency = frequency;
}
}
} |
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