LeetCode - 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.


public class LRUCache {
 
    HashMap<Integer, DoubleLinkedListNode> map;
    DoubleLinkedListNode head;
    DoubleLinkedListNode end;
    private int capacity;
    private int len;
 
    public LRUCache(int capacity) {
        this.map = new HashMap<Integer, DoubleLinkedListNode>();
        this.capacity = capacity;
        this.len = 0;
    }
 
    public int get(int key) {
        if(map.containsKey(key)) {
            DoubleLinkedListNode node = map.get(key);
            removeNode(node);
            setHead(node);
            return node.val;
        } else {
            return -1;
        }
    }

    private void removeNode(DoubleLinkedListNode node) {
        DoubleLinkedListNode pre = node.pre;
        DoubleLinkedListNode next = node.next;
        if(pre!=null) {
            pre.next = next;
        } else {
            head = next;
        }
        if(next!=null) {
            next.pre = pre;
        } else {
            end = pre;
        }
    }
 
    private void setHead(DoubleLinkedListNode node) {
        node.next = head;
        node.pre = null;
        if(head!=null) {
            head.pre = node;
        }
        head = node;
        if(end==null) {
            end = node;
        }
    }
 
    public void set(int key, int value) {
        if(map.containsKey(key)) {
            DoubleLinkedListNode oldNode = map.get(key);
oldNode.val = value;
removeNode(oldNode);
setHead(oldNode);
        } else {
            DoubleLinkedListNode newNode = new DoubleLinkedListNode(key, value);
            if(len<capacity) {
                setHead(newNode);
                map.put(newNode.key, newNode);
                len++;
            } else {
                map.remove(end.key);
                end = end.pre;
                if(end!=null) {
                    end.next = null;
                }
                setHead(newNode);
                map.put(newNode.key, newNode);
            }
        }
    }
 
    class DoubleLinkedListNode{
        int val;
        int key;
        DoubleLinkedListNode pre;
        DoubleLinkedListNode next;
     
        public DoubleLinkedListNode(int key, int val) {
            this.val = val;
            this.key = key;
        }
    }
}


public class LRUCache {
   
    private int capacity;
    private HashMap<Integer, DoubleLinkNode> map;
   
    private DoubleLinkNode head;
    private DoubleLinkNode tail;
   
    public LRUCache(int capacity) {
        this.capacity = capacity;
        this.map = new HashMap<Integer, DoubleLinkNode>();
        head = new DoubleLinkNode(0, 0);
        tail = new DoubleLinkNode(0, 0);
        head.next = tail;
        tail.pre = head;
    }
   
    private void setToHead(DoubleLinkNode node) {
        // swap to head;
        if(node.pre!=head) {
            if(node.pre!=null)
                node.pre.next = node.next;
            if(node.next!=null)
                node.next.pre = node.pre;
            DoubleLinkNode tmpNext = head.next;
            tmpNext.pre = node;
            node.next = tmpNext;
            node.pre = head;
            head.next = node;
        }
    }
   
    public int get(int key) {
        if(map.containsKey(key)) {
            DoubleLinkNode node = map.get(key);
            setToHead(node);
            return node.val;
        } else {
            // error here
            return -1;
        }
    }
   
    public void set(int key, int value) {
        if(map.containsKey(key)) {
            DoubleLinkNode node = map.get(key);
            node.val = value;
            setToHead(node);
        } else {
            if(this.map.size()==this.capacity) {
                DoubleLinkNode remove = tail.pre;
                DoubleLinkNode tmp = remove.pre;
                tail.pre = tmp;
                tmp.next = tail;
                this.map.remove(remove.key);
            }
            DoubleLinkNode node = new DoubleLinkNode(key, value);
            this.map.put(key, node);
            setToHead(node);
        }
    }
   
    static class DoubleLinkNode {
        DoubleLinkNode pre;
        DoubleLinkNode next;
        int val;
        int key;
       
        public DoubleLinkNode(int key, int val) {
            this.val = val;
            this.key = key;
        }
    }
   
}

=========

public class LRUCache {
   
    public static class DoubleLinkedList {
        DoubleLinkedList prev;
        DoubleLinkedList next;
        private int key;
        private int val;
        public DoubleLinkedList(int key, int val) {
            this.key = key;
            this.val = val;
        }
    }
   
    HashMap<Integer, DoubleLinkedList> map;
    DoubleLinkedList head;
    DoubleLinkedList tail;
    int capacity;
   
    public LRUCache(int capacity) {
        this.capacity = capacity;
        this.map = new HashMap<Integer, DoubleLinkedList>();
    }
   
    public int get(int key) {
        if (!map.containsKey(key)) return -1;
        DoubleLinkedList node = map.get(key);
        moveToFront(node);
        return node.val;
    }
   
    public void set(int key, int value) {
        if (map.containsKey(key)) {
            DoubleLinkedList node = map.get(key);
            node.val = value;
            moveToFront(node);
        } else {
            DoubleLinkedList node = new DoubleLinkedList(key, value);
            if (head == null) {
                head = node;
                tail = node;
            } else {
                node.next = head;
                head.prev = node;
                head = node;
            }
            map.put(node.key, node);
            if (map.size() > capacity) {
                map.remove(tail.key);
                tail = tail.prev;
                tail.next = null;
            }
        }
    }
   
    private void moveToFront(DoubleLinkedList node) {
        if (node == head) {
            return;
        }
        if (node == tail) {
            tail = node.prev;
        }
        DoubleLinkedList oldPrev = node.prev;
        DoubleLinkedList oldNext = node.next;
        if (oldPrev != null) {
            oldPrev.next = oldNext;
        }
        if (oldNext != null) {
            oldNext.prev = oldPrev;
        }
        node.next = head;
        head.prev = node;
        head = node;
    }

}