LRU牛客比较简单的实现

https://www.nowcoder.com/practice/5dfded165916435d9defb053c63f1e84?tpId=295&tqId=2427094&ru=/exam/oj&qru=/ta/format-top101/question-ranking&sourceUrl=%2Fexam%2Foj

public class Solution {
    Map<Integer,Integer> map;
    int capacity;
    public Solution(int capacity) {
         // write code here
        this.capacity = capacity;
        // LinkedHashMap可以保证插入有序
        map = new LinkedHashMap<>(capacity);
    }
 
    public int get(int key) {
         // write code here
        Integer value = map.get(key);
        if(value!=null){
            if(map.size()>1){
                map.remove(key);
                map.put(key,value); // 存入最后
            }
        }else{
            return -1;
        }
        return value;
    }
 
    public void set(int key, int value) {
         // write code here
        if(map.containsKey(key)){
            map.remove(key);
        }
        if(map.size()>=capacity){
            //这中相当于有一个指针，指向第一个数的前面 keySet() 返回key的集合
            //next() 取出下一个数，指针指向下一位
            Integer firstKey = map.keySet().iterator().next();
            map.remove(firstKey);
        }
        map.put(key,value);
    }
}