146. LRU Cache
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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
class LRUCache { private Map<Integer, Integer> map; private int capacity; public LRUCache(int capacity) { this.capacity = capacity; map = new LinkedHashMap<Integer, Integer>(); } public int get(int key) { Integer val = map.get(key); if (val == null) return -1; map.remove(key); map.put(key, val);//确保get后当前key变成最后一个插入的 return val; } public void put(int key, int value) { map.remove(key);//Why? Because假如update键的新value也算作visited,要先把当前key删掉重新insert确保是最后一个插入的 map.put(key, value); if (map.size() > capacity){ // for(Map.Entry<Integer, Integer> entry: map.entrySet()){ // System.out.println("key"+entry.getKey()+"value"+entry.getValue()); // } map.remove(map.entrySet().iterator().next().getKey()); } } } /** * 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); */
来自小土刀大神,短小精悍,用了LinkedHashMap的特性(保留插入顺序)。
get的时候先取出value,然后重新插入确保这个key是最后一个值。
put的时候也是要先remove了再重新put进去保证update键的情况
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