#Leet Code# LRU Cache

语言：C++

描述：使用单链表实现，HeadNode是key=-1，value=-1，next=NULL的结点。距离HeadNode近的结点是使用频度最小的Node。

 struct Node {
     int key;
     int value;
     Node* next;
 };

 class LRUCache {
 public:
     LRUCache(int capacity) {
         this->capacity = capacity;
         this->curLength = ;

         this->headNode = new Node();
         this->headNode->key = -;
         this->headNode->value = -;
         this->headNode->next = NULL;

         this->lastNode = this->headNode;
     }

     int get(int key) {
         if (this->curLength == )
             return -;

         Node* tmpNode = reSequencing(key, -);
         if (tmpNode != NULL) {
             return tmpNode->value;
         } else {
             return -;
         }
     }

     void set(int key, int value) {
         if (this->capacity == ) return;

         Node* tmpNode = reSequencing(key, value);
         if (tmpNode != NULL) {
             tmpNode->value = value;
             return;
         } 

         if (this->curLength +  > this->capacity) {
             if (this->headNode->next == this->lastNode) {
                 delete this->lastNode;
                 this->lastNode = this->headNode;
             } else {
                 Node* t = this->headNode->next->next;
                 delete this->headNode->next;
                 this->headNode->next = t;
             }
         }

         Node* newNode = new Node();
         newNode->key = key;
         newNode->value = value;
         newNode->next = NULL;

         this->lastNode->next = newNode;
         this->lastNode = newNode;

         curLength += ;
     }

     Node* reSequencing(int key, int value) {
         Node* tmpNode = this->headNode;
         Node* preNode;

         while (tmpNode != NULL) {
             if (tmpNode->key == key) {
                 break;
             }

             preNode = tmpNode;
             tmpNode = tmpNode->next;
         }

         if (tmpNode != NULL && this->lastNode->key != key) {
             preNode->next = tmpNode->next;

             this->lastNode->next = tmpNode;
             this->lastNode = tmpNode;
             tmpNode->next = NULL;
         } 

         return tmpNode;
     }

 private:
     int capacity;
     int curLength;

     Node* headNode;
     Node* lastNode;
 };