LintCode Memcache - James Pan - 博客频道 - CSDN.NET
public class Memcache {
private Map<Integer, Cache> map = new HashMap<>();
private TreeMap<Integer, List<Cache>> tm = new TreeMap<>();
public Memcache() {
// Initialize your data structure here.
}
private void expire(int curtTime) {
SortedMap<Integer, List<Cache>> hm = tm.headMap(curtTime);
for(int key : hm.keySet()) {
for(Cache cache : hm.get(key)) {
map.remove(cache.key);
}
tm.remove(key);
}
}
public int get(int curtTime, int key) {
// Write your code here
expire(curtTime);
Cache cache = map.get(key);
if (cache == null) return Integer.MAX_VALUE;
return cache.val;
}
public void set(int curtTime, int key, int value, int ttl) {
// Write your code here
expire(curtTime);
Cache cache = map.get(key);
if (cache == null) {
cache = new Cache(key, value, ttl == 0 ? Integer.MAX_VALUE : curtTime + ttl - 1);
map.put(key, cache);
List<Cache> list = tm.get(cache.ttl);
if (list == null) {
list = new ArrayList<Cache>();
tm.put(cache.ttl, list);
}
list.add(cache);
} else {
cache.val = value;
List<Cache> list = tm.get(cache.ttl);
for(int i = 0; i < list.size(); i++) {
if (list.get(i).key == key) {
list.remove(i);
break;
}
}
cache.ttl = ttl == 0 ? Integer.MAX_VALUE : curtTime + ttl - 1;
list = tm.get(cache.ttl);
if (list == null) {
list = new ArrayList<Cache>();
tm.put(cache.ttl, list);
}
list.add(cache);
}
}
public void delete(int curtTime, int key) {
// Write your code here
expire(curtTime);
Cache cache = map.get(key);
if (cache == null) return;
List<Cache> list = tm.get(cache.ttl);
for(int i = 0; i < list.size(); i++) {
if (list.get(i).key == key) {
list.remove(i);
break;
}
}
map.remove(key);
}
public int incr(int curtTime, int key, int delta) {
// Write your code here
expire(curtTime);
Cache cache = map.get(key);
if (cache == null) return Integer.MAX_VALUE;
cache.val += delta;
return cache.val;
}
public int decr(int curtTime, int key, int delta) {
// Write your code here
expire(curtTime);
Cache cache = map.get(key);
if (cache == null) return Integer.MAX_VALUE;
cache.val -= delta;
return cache.val;
}
}
class Cache {
int key;
int val;
int ttl;
Cache(int key, int val, int ttl) {
this.key = key;
this.val = val;
this.ttl = ttl;
}
}
Read full article from LintCode Memcache - James Pan - 博客频道 - CSDN.NET
Implement a memcache which support the following features:
get(curtTime, key). Get the key's value, return 2147483647 if key does not exist.set(curtTime, key, value, ttl). Set the key-value pair in memcache with a time to live (ttl). The key will be valid from curtTime to curtTime + ttl - 1 and it will be expired after ttl seconds. if ttl is 0, the key lives forever until out of memory.delete(curtTime, key). Delete the key.incr(curtTime, key, delta). Increase the key's value by delta return the new value. Return 2147483647 if key does not exist.decr(curtTime, key, delta). Decrease the key's value by delta return the new value. Return 2147483647 if key does not exist.
It's guaranteed that the input is given with increasing
curtTime.
Actually, a real memcache server will evict keys if memory is not sufficient, and it also supports variety of value types like string and integer. In our case, let's make it simple, we can assume that we have enough memory and all of the values are integers.
Search "LRU" & "LFU" on google to get more information about how memcache evict data.
Try the following problem to learn LRU cache:
http://www.lintcode.com/problem/lru-cache
http://www.lintcode.com/problem/lru-cache
get(1, 0)
>> 2147483647
set(2, 1, 1, 2)
get(3, 1)
>> 1
get(4, 1)
>> 2147483647
incr(5, 1, 1)
>> 2147483647
set(6, 1, 3, 0)
incr(7, 1, 1)
>> 4
decr(8, 1, 1)
>> 3
get(9, 1)
>> 3
delete(10, 1)
get(11, 1)
>> 2147483647
incr(12, 1, 1)
>> 2147483647class Resource { public int value; public int expired; public Resource(int value, int expired) { this.value = value; this.expired = expired; } } public class Memcache { Map<Integer, Resource> client = null; public Memcache() { // Initialize your data structure here. client = new HashMap<Integer, Resource>(); } public int get(int curtTime, int key) { // Write your code here if (!client.containsKey(key)) return Integer.MAX_VALUE; Resource res = client.get(key); if (res.expired >= curtTime || res.expired == -1) return res.value; else return Integer.MAX_VALUE; } public void set(int curtTime, int key, int value, int ttl) { // Write your code here int expired; if (ttl == 0) expired = -1; else expired = curtTime + ttl - 1; client.put(key, new Resource(value, expired)); } public void delete(int curtTime, int key) { // Write your code here if (!client.containsKey(key)) return; client.remove(key); } public int incr(int curtTime, int key, int delta) { // Write your code here if (!client.containsKey(key)) return Integer.MAX_VALUE; client.get(key).value += delta; return get(curtTime, key); } public int decr(int curtTime, int key, int delta) { // Write your code here if (!client.containsKey(key)) return Integer.MAX_VALUE; client.get(key).value -= delta; return get(curtTime, key); } }
方法：使用哈希映射保存键值对，使用有序映射保存时间戳数据。
