Method pop

chapter02/util/LinkedListX.js:48–65

()

    }
  
    pop() {
        let cur = this.head;
  
        // only one or no item exists
        if (!cur) return null;
        if (!cur.next) {
            this.head = null;
            return cur;
        }
        // move till the 2nd last
        while (cur.next.next)
            cur = cur.next;
        
        let last = this.tail;
        this.tail = cur;
        this.tail.next = null;
        return last;
    }
  
    popFirst() {
        let first = this.head;