leetcode-146.js

var Node = function(key, value, next, previous) {
    this.key = key
    this.value = value
    this.next = next
    this.previous = previous
}

/**
 * @param {number} capacity
 */
var LRUCache = function(capacity) {
    this.capacity = capacity
    this.head = null
    this.tail = null
    this.index = {}
    this.size = 0
};

/** 
 * @param {number} key
 * @return {number}
 */
LRUCache.prototype.get = function(key) {
    const node = this.index[key]
    if (!node) return -1

    // actualizamos las referencias si no es la cabeza de la lista
    this.moveToFront(node)

    return node.value
};

LRUCache.prototype.moveToFront = function(node) {
    if (node.previous) {
        // si es la cola, debemos actualizarla
        if (!node.next) this.tail = node.previous

        // interconectamos el anterior con el siguiente
        node.previous.next = node.next
        if (node.next) node.next.previous = node.previous

        // actualizamos el nodo para que quede de head
        this.head.previous = node
        node.next = this.head
        node.previous = null
        this.head = node
    }
}

/** 
 * @param {number} key 
 * @param {number} value
 * @return {void}
 */
LRUCache.prototype.put = function(key, value) {
    if (this.index[key]) {
        const node = this.index[key]
        node.value = value
        this.moveToFront(node)
    } else {
        if (this.size === this.capacity) this.evict()

        const node = new Node(key, value, this.head)
        if (this.head) {
            this.head.previous = node
            this.head = node
        } else {
            this.head = node
            this.tail = node
        }
        this.index[key] = node
        this.size++
    }
};

LRUCache.prototype.evict = function() {
    delete this.index[this.tail.key]
    this.tail = this.tail.previous
    if (!this.tail) {
        this.head = null
    } else {
        this.tail.next = null
    }
    this.size--
}