#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 = 0;

        this->headNode = new Node();
        this->headNode->key = -1;
        this->headNode->value = -1;
        this->headNode->next = NULL;

        this->lastNode = this->headNode;
    }

    int get(int key) {
        if (this->curLength == 0)
            return -1;

        Node* tmpNode = reSequencing(key, -1);  
        if (tmpNode != NULL) {
            return tmpNode->value;
        } else {
            return -1;
        }
    }

    void set(int key, int value) {
        if (this->capacity == 0) return;

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

        if (this->curLength + 1 > 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 += 1;
    }

    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;
};