#Leet Code# LRU Cache

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語言：C++

描述：使用單鏈表實現，HeadNode是key=-1，value=-1，next=NULL的結點。距離HeadNode近的結點是使用頻度最小的Node。

 1 struct Node { 2     int key; 3     int value; 4     Node* next; 5 }; 6  7 class LRUCache { 8 public: 9     LRUCache(int capacity) {10         this->capacity = capacity;11         this->curLength = 0;12 13         this->headNode = new Node();14         this->headNode->key = -1;15         this->headNode->value = -1;16         this->headNode->next = NULL;17 18         this->lastNode = this->headNode;19     }20 21     int get(int key) {22         if (this->curLength == 0)23             return -1;24 25         Node* tmpNode = reSequencing(key, -1);  26         if (tmpNode != NULL) {27             return tmpNode->value;28         } else {29             return -1;30         }31     }32 33     void set(int key, int value) {34         if (this->capacity == 0) return;35 36         Node* tmpNode = reSequencing(key, value);  37         if (tmpNode != NULL) {38             tmpNode->value = value;39             return;40         } 41 42         if (this->curLength + 1 > this->capacity) {43             if (this->headNode->next == this->lastNode) {44                 delete this->lastNode;45                 this->lastNode = this->headNode;46             } else {47                 Node* t = this->headNode->next->next;48                 delete this->headNode->next;49                 this->headNode->next = t;50             }51         }52 53         Node* newNode = new Node();54         newNode->key = key;55         newNode->value = value;56         newNode->next = NULL;57 58         this->lastNode->next = newNode;59         this->lastNode = newNode;60 61         curLength += 1;62     }63 64     Node* reSequencing(int key, int value) {65         Node* tmpNode = this->headNode;66         Node* preNode;67 68         while (tmpNode != NULL) {69             if (tmpNode->key == key) {70                 break;71             }72 73             preNode = tmpNode;74             tmpNode = tmpNode->next;75         }76 77         if (tmpNode != NULL && this->lastNode->key != key) {78             preNode->next = tmpNode->next;79 80             this->lastNode->next = tmpNode;81             this->lastNode = tmpNode;82             tmpNode->next = NULL;83         } 84 85         return tmpNode;86     }87 88 private:89     int capacity;90     int curLength;91 92     Node* headNode;93     Node* lastNode;94 };