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[LC] 146. LRU Cache

时间:2020-02-10 09:57:46      阅读:68      评论:0      收藏:0      [点我收藏+]

标签:map   could   https   sig   ons   ida   and   ati   vat   

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 int capacity;
    private Map<Integer, Node> map;
    private Node head;
    private Node tail;
    // hash map makes O(1) to get and put
    // doubly LL makes removing easier
    public LRUCache(int capacity) {
        this.map = new HashMap<>();
        this.capacity = capacity;
        this.head = null;
        this.tail = null;
    }
    
    public int get(int key) {
        Node curNode = map.get(key);
        if (curNode == null) {
            return -1;
        }

        if (tail != curNode) {
            if (curNode == head) {
                head = head.next;
            } else {                                 
                curNode.prev.next = curNode.next;
                curNode.next.prev = curNode.prev;
            }
            tail.next = curNode;
            curNode.prev = tail;
            tail = curNode;
        }
        return curNode.value;
    }
    
    public void put(int key, int value) {
        Node curNode = map.get(key);
        if (curNode != null) {
       // update the current Node, for get(), similiar with this snippet curNode.value
= value; if (tail != curNode) { if (curNode == head) { head = head.next; } else { curNode.prev.next = curNode.next; curNode.next.prev = curNode.prev; } tail.next = curNode; curNode.prev = tail; tail = curNode; } } else { Node newNode = new Node(key, value); if (capacity == 0) { Node tmp = head; head = tmp.next; map.remove(tmp.key); capacity += 1; } if (head == null && tail == null) { head = newNode; } else { tail.next = newNode; newNode.prev = tail; } tail = newNode; capacity -= 1; map.put(key, newNode); } } } class Node { int key; int value; Node prev; Node next; public Node(int key, int value) { this.key = key; this.value = value; } } /** * 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); */

 

[LC] 146. LRU Cache

标签:map   could   https   sig   ons   ida   and   ati   vat   

原文地址:https://www.cnblogs.com/xuanlu/p/12289705.html

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