leetcode Reverse Linked List II -- 重点

https://leetcode.com/problems/reverse-linked-list-ii/

understanding:

这里要注意加一个dummy node，以及index范围的确定。

my code:

class Solution(object):
def reverseBetween(self, head, m, n):
"""
:type head: ListNode
:type m: int
:type n: int
:rtype: ListNode
"""
if m == n:
return head

count = 1

m_node = head
dummy_node = ListNode(0)
pre = dummy_node

while count != m:
pre = m_node
m_node = m_node.next
count += 1
e1 = pre # end of the 1st seg
e2 = m_node # end of the 2nd set

count = 1
while count != n - m + 1:

next_node = m_node.next
m_node.next = pre
pre = m_node
m_node = next_node
count += 1
s2 = m_node.next
m_node.next = pre
s1 = m_node

e1.next = s1
e2.next = s2

if m != 1:
return head
else:
return s1

参考 code: http://bookshadow.com/weblog/2015/01/29/leetcode-reverse-linked-list-ii/