链表篇

灵神题解

 

 

class LRUCache {
    private static class Node{
        int key,value;
        Node prev,next;

        Node (int k,int v){
            key=k;
            value=v;
        }
    }
    private final int capacity;
    //哨兵节点
    private final Node dummy=new Node(0,0);
    private final Map<Integer,Node> keyToNode =new HashMap<>();

    public LRUCache(int capacity) {
        this.capacity=capacity;
        dummy.prev=dummy;
        dummy.next=dummy;
    }
    
    public int get(int key) {
           Node node=getNode(key);
           return node!=null?node.value:-1;
    }
    
    public void put(int key, int value) {
          Node node=getNode(key);
          //有书则更新
          if(node!=null){
            node.value=value;
            return;
          }
          node=new Node(key,value);
          keyToNode.put(key,node);
          //放在最上面
          pushFront(node);
          //书太多了
          if(keyToNode.size()>capacity){
              Node backNode=dummy.prev;
              keyToNode.remove(backNode.key);
              //去掉最后一本书
              remove(backNode);
          }
    }

    //取节点
    private Node getNode(int key){
        //没有这本书
        if(!keyToNode.containsKey(key)){
            return null;
        }
        //有这本书
        Node node=keyToNode.get(key);
        //抽出来
        remove(node);
        //放在最上面
        pushFront(node);
        return node;
    }

    //删除一个节点（抽出一本书）
    private void remove(Node x){
        x.prev.next=x.next;
        x.next.prev=x.prev;
    }

    //链表头添加节点
    private void pushFront(Node x){
        x.prev=dummy;
        x.next=dummy.next;
        x.prev.next=x;
        x.next.prev=x;
    }
}

/**
 * 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);
 */

 

背题