Day 86, ##, LRU Cache

LRU Cache
Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.
get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(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.
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a few improvement
#1 design a doublely-linked list class
#2 have a de-constructor
#3 code re-factory
用了2个dummy， head跟tail

struct LinkedNode {
    int key;
    int val;
    LinkedNode *pre;
    LinkedNode *next;
    LinkedNode(int key,int val) {
        this->key = key;
        this->val = val;
        pre = NULL;
        next = NULL;
    }
};

class LRUCache{
public:
    LRUCache(int capacity) {
        this->capacity = capacity;
        size = 0;
        head = new LinkedNode(-1,-1);
        tail = new LinkedNode(-1,-1);
        head->next = tail;
        tail->pre = head;
    }
    
    int get(int key) {
        if (dic.find(key) == dic.end()) {
            return -1;
        }
        LinkedNode *node = removeNode(dic[key]);
        insertToFront(node);
        return node->val;
    }
    
    LinkedNode* removeNode(LinkedNode *node) {
        LinkedNode *preNode = node->pre;
        LinkedNode *nextNode = node->next;
        preNode->next = nextNode;
        nextNode->pre = preNode;
        return node;
    }
    
    void insertToFront(LinkedNode *node) {
        LinkedNode *temp = head->next;
        head->next = node;
        temp->pre = node;
        node->next = temp;
        node->pre = head;
    }
    
    void set(int key, int value) {
        if (dic.find(key) == dic.end()) {
            LinkedNode *temp = head->next;
            LinkedNode *add = new LinkedNode(key,value);
            head->next = add;
            add->pre = head;
            add->next = temp;
            temp->pre = add;
            dic[key] = add;
            size++;
        }else {
            LinkedNode *catched = removeNode(dic[key]);
            insertToFront(dic[key]);
            dic[key]->val = value;
        }
        
        if (size > capacity) {
            LinkedNode *catched = removeNode(tail->pre);
            dic.erase(catched->key);
            delete catched;
            size--;
        }
    }
private:
    int capacity;
    int size;
    LinkedNode *head;
    LinkedNode *tail;
    unordered_map<int,LinkedNode*> dic;
};

Java, updated on Jun-30th-2018

class LRUCache {
    private int capacity;
    private DoublyLinkedNode head;
    private DoublyLinkedNode tail;
    private Map<Integer, DoublyLinkedNode> map;
    
    public LRUCache(int capacity) {
        this.capacity = capacity;
        head = new DoublyLinkedNode(-1, -1);
        tail = new DoublyLinkedNode(-1, -1);
        head.next = tail;
        tail.pre = head;
        map = new HashMap<>();
    }
    
    public int get(int key) {
        if (map.containsKey(key)) {
            DoublyLinkedNode node = pickupAndReturn(key);
            insertFront(node);
            return node.val;
        }
        
        return -1;
    }
    
    public void put(int key, int value) {
        DoublyLinkedNode node = null;
        if (!map.containsKey(key)) {
            node = new DoublyLinkedNode(key, value);
            map.put(key, node);
        }else {
            node = pickupAndReturn(key);
            node.val = value;
        }
        
        insertFront(node);
        
        if (map.size() > capacity) {
            removeLast();
        }
    }
    
    private void removeLast() {
        int key = tail.pre.key;
        tail.pre.pre.next = tail;
        tail.pre = tail.pre.pre;
        map.remove(key);
    }
    
    private void insertFront(DoublyLinkedNode node) {
        head.next.pre = node;
        node.next = head.next;
        head.next = node;
        node.pre = head;
    }
    
    private DoublyLinkedNode pickupAndReturn(int key) {
        DoublyLinkedNode node = map.get(key);
        node.pre.next = node.next;
        node.next.pre = node.pre;

        return node;
    }
}

class DoublyLinkedNode{
    public DoublyLinkedNode pre;
    public DoublyLinkedNode next;
    public int key;
    public int val;
    
    public DoublyLinkedNode(int key, int val) {
        this.key = key;
        this.val = val;
    }
}

/**
 * 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);
 */