// 2. 링크드리스트
function LinkedList() {
  this.length = 0;
  this.head = null;
}

// 노드
function Node(v) {
  this.v = v;
  this.next = null;
}

// 추가
LinkedList.prototype.append = function(v) {
  var node = new Node(v);
  var current;

  if(this.head) {
    current = this.head;

    while(current.next) {
      current = current.next;
    }

    current.next = node;
  } else {
    this.head = node;
  }

  this.length++;
}

LinkedList.prototype.removeAt = function(p) {
  var current = this.head;
  var prev, idx = 0;

  if (p >= 0 && p < this.length) {
    while(idx < this.length) {
      if(idx === p) {
        prev.next = current.next;
        this.length--;
        return current.v;
      } else {
        prev = current;
        current = current.next;
        idx++;
      }
    }
  }

  return null;
}