--- /dev/null
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+ value: true
+});
+exports.default = DLL;
+// Simple doubly linked list (https://en.wikipedia.org/wiki/Doubly_linked_list) implementation
+// used for queues. This implementation assumes that the node provided by the user can be modified
+// to adjust the next and last properties. We implement only the minimal functionality
+// for queue support.
+function DLL() {
+ this.head = this.tail = null;
+ this.length = 0;
+}
+
+function setInitial(dll, node) {
+ dll.length = 1;
+ dll.head = dll.tail = node;
+}
+
+DLL.prototype.removeLink = function (node) {
+ if (node.prev) node.prev.next = node.next;else this.head = node.next;
+ if (node.next) node.next.prev = node.prev;else this.tail = node.prev;
+
+ node.prev = node.next = null;
+ this.length -= 1;
+ return node;
+};
+
+DLL.prototype.empty = DLL;
+
+DLL.prototype.insertAfter = function (node, newNode) {
+ newNode.prev = node;
+ newNode.next = node.next;
+ if (node.next) node.next.prev = newNode;else this.tail = newNode;
+ node.next = newNode;
+ this.length += 1;
+};
+
+DLL.prototype.insertBefore = function (node, newNode) {
+ newNode.prev = node.prev;
+ newNode.next = node;
+ if (node.prev) node.prev.next = newNode;else this.head = newNode;
+ node.prev = newNode;
+ this.length += 1;
+};
+
+DLL.prototype.unshift = function (node) {
+ if (this.head) this.insertBefore(this.head, node);else setInitial(this, node);
+};
+
+DLL.prototype.push = function (node) {
+ if (this.tail) this.insertAfter(this.tail, node);else setInitial(this, node);
+};
+
+DLL.prototype.shift = function () {
+ return this.head && this.removeLink(this.head);
+};
+
+DLL.prototype.pop = function () {
+ return this.tail && this.removeLink(this.tail);
+};
+module.exports = exports["default"];
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