leetcode 146. LRU Cache
Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.
get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(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.
The cache is initialized with a positive capacity.
Follow up:
Could you do both operations in O(1) time complexity?
Example:
LRUCache cache = new LRUCache( 2 /* capacity */ );
cache.put(1, 1);
cache.put(2, 2);
cache.get(1); // returns 1
cache.put(3, 3); // evicts key 2
cache.get(2); // returns -1 (not found)
cache.put(4, 4); // evicts key 1
cache.get(1); // returns -1 (not found)
cache.get(3); // returns 3
cache.get(4); // returns 4
- 思路：用链表存内容，然后用散列表存映射关系
C++
class LRUCache {
public:
int size;
list<int> lru;
unordered_map<int, list<int>::iterator> mp;
unordered_map<int, int> kv;
LRUCache(int capacity) {
size=capacity;
}
void touch(int key){
if(kv.count(key))
lru.erase(mp[key]);
lru.push_front(key);
mp[key]=lru.begin();
}
int get(int key) {
if(kv.count(key)==0)return -1;
touch(key);
return kv[key];
}
void put(int key, int value) {
if(kv.size()==size&&kv.count(key)==0){// full
mp.erase(lru.back());
kv.erase(lru.back());
lru.pop_back();
}
touch(key);
kv[key]=value;
}
};
/**
* Your LRUCache object will be instantiated and called as such:
* LRUCache* obj = new LRUCache(capacity);
* int param_1 = obj->get(key);
* obj->put(key,value);
*/
Java
class LRUCache {
private Map<Integer,ListNode> lru;
ListNode head=null;
ListNode tail=null;
int c;
public LRUCache(int _c) {
this.c=_c;
lru=new HashMap<Integer,ListNode>();
}
public int get(int key) {
if(lru.containsKey(key)) {
ListNode t=lru.get(key);
t.update();
return t.v;
} else return -1;
}
public void put(int key, int value) {
if(lru.containsKey(key)) {
ListNode t=lru.get(key);
t.v=value;
t.update();
} else {
if(c==0)return;
if(lru.size()==c){
lru.remove(head.k);
head.remove();
}
ListNode tmp=new ListNode(key,value);
tmp.append();
lru.put(key,tmp);
}
}
class ListNode {
int k,v;
ListNode pre=null,nxt=null;
public ListNode(int _k,int _v){
this.k=_k;
this.v=_v;
}
private void update() {
if(tail==this)return;
if(this!=head)
this.pre.nxt=this.nxt;
else
head=this.nxt;
this.nxt.pre=this.pre;
this.append();
}
private void append(){
if(tail==null){
head=this;
tail=this;
} else {
this.nxt=null;
this.pre=tail;
tail.nxt=this;
tail=this;
}
}
private void remove(){
if(tail==this) {
head=null;
tail=null;
} else {
head=this.nxt;
head.pre=null;
}
}
}
}
/**
* Your LRUCache object will be instantiated and called as such:
* LRUCache obj = new LRUCache(capacity);
* int param_1 = obj.get(key);
* obj.put(key,value);
*/
