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); */
标签：map could https sig ons ida and ati vat
原文地址：https://www.cnblogs.com/xuanlu/p/12289705.html
