146-LRU-Cache.js

/** 
 * https://leetcode.com/problems/lru-cache/
 * Time O(1) | Space O(N)
 * Your LRUCache object will be instantiated and called as such:
 * var obj = new LRUCache(capacity)
 * var param_1 = obj.get(key)
 * obj.put(key,value)
 */
 class LRUCache {
    constructor(capacity) {
        this.capacity = capacity;
        this.map = new Map();

        this.head = {};
        this.tail = {};

        this.head.next = this.tail;
        this.tail.prev = this.head;
    }

    removeLastUsed () {
        const [ key, next, prev ]  = [ this.head.next.key, this.head.next.next, this.head ];

        this.map.delete(key);
        this.head.next = next;
        this.head.next.prev = prev;
    }

    put (key, value) {
        const hasKey = this.get(key) !== -1;
        const isAtCapacity = this.map.size === this.capacity;
        
        if (hasKey) return (this.tail.prev.value = value);
        if (isAtCapacity) this.removeLastUsed();

        const node = { key, value };
        this.map.set(key, node);
        this.moveToFront(node);
    }

    moveToFront (node) {
        const [ prev, next ] = [ this.tail.prev, this.tail ];

        this.tail.prev.next = node;
        this.connectNode(node, { prev, next });
        this.tail.prev = node;
    }

    connectNode (node, top) {
        node.prev = top.prev;
        node.next = top.next;
    }

    get (key) {
        const hasKey = this.map.has(key);
        if (!hasKey) return -1;

        const node = this.map.get(key);
        
        this.disconnectNode(node);
        this.moveToFront(node);

        return node.value;
    }

    disconnectNode (node) {
        node.next.prev = node.prev;
        node.prev.next = node.next;
    }
}