>[success] # 循環鏈表 ~~~ 1.循環鏈表就是將鏈尾連接到鏈頭，也就是說'尾結點指向的不在是null而是頭結點'，形成首尾相連的效果 2.需要處理環形結構時候可以使用'循環鏈表' ~~~ >[danger] ##### 代碼 ~~~ class CircularLinkedList extends LinkedList { constructor(equalsFn = defaultEquals) { super(equalsFn); } push(element) { const node = new Node(element); let current; if (this.head == null) { this.head = node; } else { current = this.getElementAt(this.size() - 1); current.next = node; } // set node.next to head - to have circular list node.next = this.head; this.count++; } insert(element, index) { if (index >= 0 && index <= this.count) { const node = new Node(element); let current = this.head; if (index === 0) { if (this.head == null) { // if no node in list this.head = node; node.next = this.head; } else { node.next = current; current = this.getElementAt(this.size()); // update last element this.head = node; current.next = this.head; } } else { const previous = this.getElementAt(index - 1); node.next = previous.next; previous.next = node; } this.count++; return true; } return false; } removeAt(index) { if (index >= 0 && index < this.count) { let current = this.head; if (index === 0) { if (this.size() === 1) { this.head = undefined; } else { const removed = this.head; current = this.getElementAt(this.size() - 1); this.head = this.head.next; current.next = this.head; current = removed; } } else { // no need to update last element for circular list const previous = this.getElementAt(index - 1); current = previous.next; previous.next = current.next; } this.count--; return current.element; } return undefined; } } ~~~