思路

使用内置LinkedHashMap

class LRUCache extends LinkedHashMap<Integer,Integer>{
    private int capacity;
    public LRUCache(int capacity){
        super(capacity,0.75f,true);
        this.capacity=capacity;
    }
    public int get(int key){
        return super.getOrDefault(key,-1);
    }
    public void put(int key,int value){
        super.put(key, value);
    }
    @Override
    protected boolean removeEldestEntry(Map.Entry<Integer, Integer> eldest) {
        return size() > capacity; 
    }
}