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// Design

// Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.

// get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
// put(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.

// The cache is initialized with a positive capacity.

// Follow up:
// Could you do both operations in O(1) time complexity?

// Example:

// LRUCache cache = new LRUCache( 2 /* capacity */ );

// cache.put(1, 1);
// cache.put(2, 2);
// cache.get(1);       // returns 1
// cache.put(3, 3);    // evicts key 2
// cache.get(2);       // returns -1 (not found)
// cache.put(4, 4);    // evicts key 1
// cache.get(1);       // returns -1 (not found)
// cache.get(3);       // returns 3
// cache.get(4);       // returns 4

class LRUCache {
    private Map<Integer, DLinkNode> cache;
    DLinkNode tail = null;
    DLinkNode head = null;
    int capacity;

    public LRUCache(int capacity) {
        cache = new HashMap<Integer, DLinkNode>();
        this.capacity = capacity;
    }
    
    public int get(int key) {
        if (cache.containsKey(key)) {
            DLinkNode target = cache.get(key);
            int value = target.value;
            target.update();
            return value;
        }
        else return -1;
    }
    
    public void put(int key, int value) {
        if (cache.containsKey(key)) {
            DLinkNode target = cache.get(key);
            target.value = value;
            target.update();
        }
        else {
            if (capacity == 0) return;
            if (cache.size() == capacity) {
                cache.remove(head.key);
                head.removeFromHead();
            }
            DLinkNode newNode = new DLinkNode(key, value);
            newNode.append();
            cache.put(key, newNode);
        }
    }
    
    class DLinkNode {
        int key;
        int value;
        DLinkNode left = null;
        DLinkNode right = null;
        
        public DLinkNode(int key, int value) {
            this.key = key;
            this.value = value;
        }
        
        private void removeFromHead() {
            if (tail == this) {
                head = null;
                tail = null;
            }
            else {
                head = this.right;
                head.left = null;
            }
        }
        
        private void update() {
            if (tail == this) return;
            else {
                if (this != head) {
                    this.left.right = this.right;
                }
                else {
                    head = this.right;
                }
                this.right.left = this.left;
                this.append();
            }
        }
        
        private void append() {
            if (tail == null) {
                head = this;
                tail = this;
            }
            else {
                this.right = null;
                this.left = tail;
                tail.right = this;
                tail = this;
            }
        }
    }
}

/**
 * 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);
 */