leetcode 146: LRU Cache

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Use an unordered map and a doubly linked list to implement.

struct Node{    int key;    int value;    Node* next;    Node* pre;    Node(int k,int v){        key=k;        value=v;        pre=next=NULL;    }};class LRUCache{public:    LRUCache(int capacity) {        cap=capacity;        cachesize=0;        head=new Node(0,0);        tail=new Node(0,0);        head->next=tail;        tail->pre=head;    }        int get(int key) {        if(mp.find(key)!=mp.end())        {            Node *p=mp[key];            p->next->pre=p->pre;            p->pre->next=p->next;                        p->pre=tail->pre;            tail->pre->next=p;            p->next=tail;            tail->pre=p;            return mp[key]->value;        }        return -1;    }        void set(int key, int value) {        unordered_map<int,Node*>::iterator it=mp.find(key);        if(it!=mp.end())        {            Node *p=mp[key];            p->next->pre=p->pre;            p->pre->next=p->next;            p->value=value;                        p->pre=tail->pre;            tail->pre->next=p;            p->next=tail;            tail->pre=p;        }        else        {            if(cachesize==cap)            {                it=mp.find(head->next->key);                Node *p=head->next;                head->next->next->pre=head;                head->next=head->next->next;                delete p;                mp.erase(it);                cachesize--;            }            Node *p=new Node(key,value);            p->pre=tail->pre;            tail->pre->next=p;            p->next=tail;            tail->pre=p;            mp.insert(make_pair(key,p));            cachesize++;        }    }private:    unordered_map<int,Node*> mp;    Node* head;    Node* tail;    int cachesize;    int cap;};

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