【算法】反转链表

while 判断当前指针是否为空

const reverseList = (head) => {
  let pre = null;
  let cur = head;

  while (cur != null) {
    let next = cur.next;  // 存储下一个节点
    cur.next = pre;        //  翻转
    pre = cur;               // 
    cur = next;             // cur 设置成next 下一轮循环
  }
  return pre;
};