1.   快指针 = head
    2.   慢指针 = head
    3.   while(快指针.next){
    4.       if(N-- <= 0){
    5.           慢指针 = 慢指针.next
    6.       }
    7.       快指针 = 快指针.next
    8.   }
    1. // 取中间的
    2. let fast = head,slow=head
    3. while(fast.next){
    4.   fast = fast.next
    5.   if (fast.next) fast = fast.next
    6.   slow= slow.next
    7. }
    1.     let start = head
    2.   let fast = head
    3.   let slow = head
    4.   while(fast && fast.next){
    5.     fast = fast.next.next;
    6.     slow = slow.next;
    7.     if (slow==fast){
    8.       while(slow != start){
    9.         slow= slow.next
    10.         start = start.next
    11.       }
    12.       return start
    13.     }
    14.   }
    • 找到链表的倒数第k位
    • 求一个有序链表的值域的中位数
    • 判断循环链表的循环入口位置