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// 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.
export default 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);
};
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