146.lru-cache.java

import java.util.HashMap;
import java.util.Map;

// @lc code=start
class Node {
    int key, value;
    Node prev, next;

    Node(int key, int value) {
        this.key = key;
        this.value = value;
    }
}

class LRUCache {

    private final Node head = new Node(0, 0);
    private final Node tail = new Node(0, 0);
    private final Map<Integer, Node> map = new HashMap<>();
    private final int capacity;

    public LRUCache(int capacity) {
        this.capacity = capacity;
        head.next = tail;
        tail.prev = head;
    }

    public int get(int key) {
        if (!map.containsKey(key)) {
            return -1;
        }

        Node node = map.get(key);
        moveToFront(node);
        return node.value;
    }

    public void put(int key, int value) {
        if (map.containsKey(key)) {
            Node node = map.get(key);
            node.value = value;
            moveToFront(node);
        } else {
            if (map.size() == capacity) {
                evict();
            }

            Node node = new Node(key, value);
            map.put(key, node);
            insertFront(node);
        }
    }

    private void insertFront(Node node) {
        node.next = head.next;
        node.prev = head;
        head.next.prev = node;
        head.next = node;
    }

    private void remove(Node node) {
        node.prev.next = node.next;
        node.next.prev = node.prev;
    }

    private void moveToFront(Node node) {
        remove(node);
        insertFront(node);
    }

    private void evict() {
        Node lru = tail.prev;
        remove(lru);
        map.remove(lru.key);
    }
}
// @lc code=end

/**
 * 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 app=leetcode id=146 lang=java
 *
 * [146] LRU Cache
 */

// @lc code=start