Day4：Leetcode-92. Reverse Linked List

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于 2021-09-22 20:18:39 发布

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分类专栏： Leetcode经典题，C++、Python双解文章标签： leetcode list 链表

本文链接：https://blog.youkuaiyun.com/qq_39679069/article/details/120422107

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本文介绍了一种反转链表中指定区间元素的方法。通过定义辅助节点并遍历到左边界节点，再将右边界内的节点进行反转操作，最终实现区间内元素的反转。此算法适用于计算机科学中的数据结构学习。

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Sloution 1:

split the linked list,then joint it, pay attention to the boundary

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:

    def reverseBetween(self, head: ListNode, left: int, right: int) -> ListNode:
        def reverse(head):
            pre = None
            cur = head
            while cur:
                next = cur.next
                cur.next = pre
                pre = cur
                cur = next
            return cur
        dummy_node = ListNode(-1,head)

        pre = dummy_node
        for i in range(left-1):  #pre is the node before leftnode
            pre = pre.next
        right_node = pre
        for i in range(right-left+1): #right_node is truly rightnode
            right_node = right_node.next

        left_node = pre.next
        curr = right_node.next

        pre.next = None
        
        right_node.next = None

        reverse(left_node)
        pre.next = right_node
        left_node.next = curr
    
        return dummy_node.next