[LeetCode]206. Reverse Linked List

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于 2015-05-09 05:11:16 发布

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本文链接：https://blog.youkuaiyun.com/myself9711/article/details/45596973

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本文深入解析了单链表反转算法的两种实现方式：递归和迭代。详细介绍了每种方法的原理、步骤，并通过代码示例进行演示。适合计算机科学与软件工程领域的学习者。

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Reverse a singly linked list.

Solution: 创建before, cur, after指针。

Time Complexity: O(n)

Solution1: Recursive

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

class Solution:
    # @param {ListNode} head
    # @return {ListNode}

    def __init__(self):
        self.before = None

    def reverseList(self, head):
        cur = head
        if cur is None:
            return self.before
        after = cur.next
        cur.next = self.before
        self.before = cur
        cur = after
        return self.reverseList(cur) #don't forget 'return' here

Solution2: Iteration.

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

class Solution:
    # @param {ListNode} head
    # @return {ListNode}
    def reverseList(self, head):
        if head is None or head.next is None:
            return head
        before = None
        cur = head
        while cur is not None:
            after = cur.next
            cur.next = before
            before = cur
            cur = after
        return before