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LRUCache.java
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LRUCache.java
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import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.*;
public class LRUCache {
private static class Cache {
private class Entry implements Comparable<Entry> {
String key;
String value;
Entry next;
Entry prev;
public Entry(String key, String value) {
this.key = key;
this.value = value;
}
public int compareTo(Entry e) {
return this.key.compareTo(e.key);
}
}
private Map<String, Entry> cacheMap = new HashMap<String, Entry>();
private int size;
private Entry head;
private Entry tail;
public Cache() {
}
public void setCacheSize(int size) {
this.size = size;
adjustCacheSize();
}
public void insertEntry(String key, String value) {
if (cacheMap.containsKey(key)) {
Entry e = getFromCache(key);
e.value = value;
return;
}
Entry e = new Entry(key, value);
if (head == null) {
head = e;
tail = e;
} else {
e.next = head;
head.prev = e;
head = e;
}
cacheMap.put(key, e);
if (cacheMap.size() > size) {
removeEntry();
}
}
public void removeEntry() {
if (tail == null)
return;
Entry e = tail;
if (tail.prev != null) {
tail.prev.next = null;
tail = tail.prev;
}
e.next = null;
e.prev = null;
cacheMap.remove(e.key);
}
public void getEntry(String key, boolean modify) {
Entry e = null;
if (cacheMap.containsKey(key)) {
if (modify)
e = getFromCache(key);
else
e = cacheMap.get(key);
System.out.println(e.value);
} else {
System.out.println("NULL");
}
}
public void dumpCache() {
TreeSet<Entry> sortedEntry = new TreeSet<Entry>();
Entry current = head;
while (current != null) {
sortedEntry.add(current);
current = current.next;
}
for (Entry e : sortedEntry) {
System.out.println(e.key + " " + e.value);
}
}
private void adjustCacheSize() {
while (cacheMap.size() > size) {
removeEntry();
}
}
private Entry getFromCache(String key) {
Entry e = cacheMap.get(key);
if (e.prev != null) {
{
e.prev.next = e.next;
if (e.next != null) {
e.next.prev = e.prev;
} else {
tail = e.prev;
}
e.prev = null;
e.next = head;
head.prev = e;
head = e;
}
}
return e;
}
}
static void readInput() throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String str = br.readLine();
int numberOfCommands = Integer.parseInt(str);
String[] command;
Cache cache = new Cache();
while (numberOfCommands > 0) {
str = br.readLine();
command = str.split(" ");
char commandChar = command[0].charAt(0);
switch (commandChar) {
case 'B':
cache.setCacheSize(Integer.parseInt(command[1]));
break;
case 'S':
cache.insertEntry(command[1], command[2]);
break;
case 'G':
cache.getEntry(command[1], true);
break;
case 'P':
cache.getEntry(command[1], false);
break;
case 'D':
cache.dumpCache();
break;
}
numberOfCommands--;
}
br.close();
}
public static void main(String[] args) {
try {
readInput();
} catch (Exception e) {
System.err.println("Error:" + e.getMessage());
}
}
}