LeetCode 146. LRU缓存机制

[碎碎酱]

题目

https://leetcode-cn.com/problems/lru-cache/submissions/

思路

1. 使用Map记录缓存值, 使用链表记录缓存操作顺序, 最后操作的缓存置于链表头部, 链表尾部就是最少操作的缓存
2. 读取缓存时, 更新缓存操作顺序, 将缓存节点从链表中移除, 再将其添加到链表头部. 移除节点时要保证链表的连续性, 为了在O(1)时间完成该操作, 需要使用双向链表
3. 设置缓存时, 如果是已存在的缓存, 则直接更新缓存值即可, 并更新缓存操作顺序. 如果是不存在的缓存, 将缓存加到链表头部, 添加后如果缓存超过了上限, 则将链表尾部的缓存清除掉

代码

class DoubleLinkList {
    constructor() {
        this.head = null;
        this.tail = null;
        this.length = 0;
    }

    unshift(node) {
        if (this.head && this.tail) {
            node.prev = null;
            node.next = this.head;
            this.head.prev = node;
            this.head = node;
        } else {
            node.prev = node.next = null;
            this.head = this.tail = node;
        }

        this.length++;
        return node;
    }

    pop() {
        if (this.tail) {
            const node = this.tail;
            if (this.head === this.tail) {
                this.head = this.tail = null;
            } else {
                this.tail.prev.next = null;
                this.tail = this.tail.prev;
            }
            this.length--;
            return node;
        }
    }

    remove(node) {
        if (node !== this.head && node !== this.tail) {
            node.prev.next = node.next;
            node.next.prev = node.prev;
        }
        if (node === this.head) {
            this.head = this.head.next;
        }
        if (node === this.tail) {
            this.tail = this.tail.prev;
        }
        this.length--;
    }
}

class LRUCache {
    constructor(capacity) {
        this.capacity = capacity;
        this.list = new DoubleLinkList();
        this.map = new Map();
    }

    get(key) {
        let node = this.map.get(key);
        if (node) {
            this.list.remove(node);
            this.list.unshift(node);
            return node.value;
        } else {
            return -1;
        }
    }

    put(key, value) {
        let node = this.map.get(key);
        if (node) {
            node.value = value;
            this.list.remove(node);
            this.list.unshift(node);
        } else {
            node = { key, value };
            this.list.unshift(node);
            this.map.set(key, node);
            if (this.list.length > this.capacity) {
                const tail = this.list.pop();
                this.map.delete(tail.key);
            }
        }
    }
}

[落落落洛克]

Map这种数据结构本身遍历是有顺序的 按照插入的顺序遍历 所以可以不用链表来记住顺序