leetcode 92. 反转链表 II

class Solution(object):
	def reverseBetween(self, head, left, right):
		"""
		:type head: ListNode
		:type left: int
		:type right: int
		:rtype: ListNode
		"""    
		right = right -1
		left = left -1
 
		while( right-left>=0 ):
			print(right-left)
			# 左侧节点
			l = head
			for i in range(left):
				l = l.next
			# 右侧节点
			r = head
			for i in range(right):
				r = r.next
			# print(l.val, r.val)
			l.val, r.val = r.val, l.val
			right = right-1
			left = left+1
		print(head)
		return head

上面的方法其实有那么些问题，更ok的应该是下面这种

class Solution:
    def reverseBetween(self, head: ListNode, left: int, right: int) -> ListNode:
        # 设置 dummyNode 是这一类问题的一般做法
        dummy_node = ListNode(-1)
        dummy_node.next = head
        pre = dummy_node
        for _ in range(left - 1):
            pre = pre.next
 
        cur = pre.next
        for _ in range(right - left):
            next = cur.next
            cur.next = next.next
            next.next = pre.next
            pre.next = next
        return dummy_node.next