链表

1. 链表概念
2. 链表建立

class ListNode(object):
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
listnode1 = new ListNode(-1)
listnode2 = new ListNode(-1)

3. 查，删，增

编写程序以 x 为基准分割链表，使得所有小于 x 的节点排在大于或等于 x 的节点之前。如果链表中包含 x，x 只需出现在小于 x 的元素之后(如下所示)。分割元素 x 只需处于“右半部分”即可，其不需要被置于左右两部分之间

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/partition-list-lcci
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
class ListNode(object):
     def __init__(self, val=0, next=None):
          self.val = val
          self.next =next

listnode1 =  ListNode(-1)
listnode2 =  ListNode(-1)
dummy1 = listnode1
dummy2 = listnode2
p = head
while p != None:
    if dummy1.val < x:
        dummy1.next = p
        dummy1 =  dummy1.next 
    else:
        dummy2.next = p
        dummy2 =  dummy2.next 
    p = p.next

if listnode1 == None:
    return head
else:
    dummy1.next = listnode2.next
    dummy2.next = None
    return dummy1.next

4. 反转
   https://leetcode-cn.com/problems/fan-zhuan-lian-biao-lcof/
5. 排序
   https://leetcode-cn.com/problems/insertion-sort-list/
6. 环，相交，合并
   https://leetcode-cn.com/problems/intersection-of-two-linked-lists/
   https://leetcode-cn.com/problems/middle-of-the-linked-list/
   合并：
   https://leetcode-cn.com/problems/merge-two-sorted-lists/
7. 分割