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[leetcode] problem 146 – lru cache

admin 11月 13, 2020 0

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.

Follow up

Could you do both operations in O(1) time complexity?

Example

LRUCache cache = new LRUCache( 2  );

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

Code

private Map<Integer, Integer> map;

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

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

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