LeetCode : 146. LRU Cache 最近最少访问

试题
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

代码
最简单的就是get或put后到将值重新插入到hash里。

class LRUCache {
    int capacity;
    LinkedHashMap<Integer, Integer> hash;
    
    public LRUCache(int capacity) {
        this.capacity = capacity;
        this.hash = new LinkedHashMap<>();
    }
    
    public int get(int key) {
        Integer val = hash.get(key);
        if(val == null){
            return -1;
        }
        hash.remove(key);
        hash.put(key, val);
        return val;   
    }
    
    public void put(int key, int value) {
        hash.remove(key);
        hash.put(key, value);
        if(hash.size() > capacity){
            hash.remove(hash.keySet().iterator().next());
        }
    }
}

/**
 * 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);
 */

public class LRUCache {
    Map<Integer, Integer> map;

    public LRUCache(int capacity) {
        this.map = new LinkedHashMap<Integer, Integer>(128, 0.75f, true) {
            protected boolean removeEldestEntry(Map.Entry<Integer, Integer> eldest) {
                return size() > capacity;
            }
        };
    }

    public int get(int key) {
        return map.getOrDefault(key, -1);
    }

    public void put(int key, int value) {
        map.put(key, value);
    }
}