146.lru-cache.cpp

/*
 * @lc app=leetcode id=146 lang=cpp
 *
 * [146] LRU Cache
 *
 * https://leetcode.com/problems/lru-cache/description/
 *
 * algorithms
 * Medium (35.07%)
 * Likes:    7893
 * Dislikes: 323
 * Total Accepted:    713K
 * Total Submissions: 2M
 * Testcase Example:  '["LRUCache","put","put","get","put","get","put","get","get","get"]\n[[2],[1,1],[2,2],[1],[3,3],[2],[4,4],[1],[3],[4]]'
 *
 * Design a data structure that follows the constraints of a Least Recently
 * Used (LRU) cache.
 * 
 * Implement the LRUCache class:
 * 
 * 
 * LRUCache(int capacity) Initialize the LRU cache with positive size
 * capacity.
 * int get(int key) Return the value of the key if the key exists, otherwise
 * return -1.
 * void put(int key, int value) Update the value of the key if the key exists.
 * Otherwise, add the key-value pair to the cache. If the number of keys
 * exceeds the capacity from this operation, evict the least recently used
 * key.
 * 
 * 
 * Follow up:
 * Could you do get and put in O(1) time complexity?
 * 
 * 
 * Example 1:
 * 
 * 
 * Input
 * ["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"]
 * [[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]
 * Output
 * [null, null, null, 1, null, -1, null, -1, 3, 4]
 * 
 * Explanation
 * LRUCache lRUCache = new LRUCache(2);
 * lRUCache.put(1, 1); // cache is {1=1}
 * lRUCache.put(2, 2); // cache is {1=1, 2=2}
 * lRUCache.get(1);    // return 1
 * lRUCache.put(3, 3); // LRU key was 2, evicts key 2, cache is {1=1, 3=3}
 * lRUCache.get(2);    // returns -1 (not found)
 * lRUCache.put(4, 4); // LRU key was 1, evicts key 1, cache is {4=4, 3=3}
 * lRUCache.get(1);    // return -1 (not found)
 * lRUCache.get(3);    // return 3
 * lRUCache.get(4);    // return 4
 * 
 * 
 * 
 * Constraints:
 * 
 * 
 * 1 <= capacity <= 3000
 * 0 <= key <= 3000
 * 0 <= value <= 10^4
 * At most 3 * 10^4 calls will be made to get and put.
 * 
 * 
 */

// @lc code=start
class LRUCache {
public:
    LRUCache(int capacity) {
        this->capacity = capacity;
        root = new ListNode();
        tail = root;
    }
    
    int get(int key) {
        if (lruMap.count(key)) {
             moveForward(root, lruMap[key]);
             return lruMap[key]->value;
        }
        return -1;
    }
    
    void put(int key, int value) {
        if (lruMap.count(key)) {
            lruMap[key]->value = value;
            moveForward(root, lruMap[key]);
        } else {
            ListNode* newNode = new ListNode(key, value);
            if (capacity == lruMap.size()) {
                //lruMap[tail->key] = nullptr;
                lruMap.erase(tail->key);
                remove(tail, true);
            }
            insert(root, newNode);
            lruMap[key] = newNode;
        }
    }
private:
    struct ListNode {
        int key;
        int value;
        ListNode* next;
        ListNode* last;
        ListNode() : key(-1), value(-1), last(nullptr), next(nullptr) { }
        ListNode(int k, int v) : key(k), value(v), last(nullptr), next(nullptr) { }
    };
    
    int capacity;
    unordered_map<int, ListNode*> lruMap;
    ListNode* root;
    ListNode* tail;
    
    void moveForward(ListNode* root, ListNode* node) {
        if (!root || !node)
            return;
        remove(node);
        insert(root, node);
    }
    
    void insert(ListNode* root, ListNode* node) {
        if (!root || !node)
            return ;
        if (tail == root)
            tail = node;
        node->last = root;
        node->next = root->next;
        if (root->next)
            root->next->last = node;
        root->next = node;
    }
    
    void remove(ListNode* node, bool destroyed = false) {
        if (!node)
            return;
        if (node == tail)
            tail = node->last;
        node->last->next = node->next;
        if (node->next)
            node->next->last = node->last;
        if (destroyed)
            delete node;
    }
};

/**
 * 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);
 */
// @lc code=end