代码随想录算法公开课day4

最新推荐文章于 2025-05-27 21:52:10 发布

邪王真眼小鸟游六花

最新推荐文章于 2025-05-27 21:52:10 发布

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文章标签：算法

本文链接：https://blog.youkuaiyun.com/weixin_52450371/article/details/144343841

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206. 反转链表 - 力扣（LeetCode）

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        pre = None
        cur = head
        while cur:
            temp = cur.next
            cur.next = pre
            pre = cur
            cur = temp
        return pre

# 递归

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        return self.reverse(head,None)
    def reverse(self,cur,pre):
        if cur == None:
            return pre
        temp = cur.next
        cur.next = pre
        pre = cur
        cur = temp
        return self.reverse(cur,pre)

24. 两两交换链表中的节点 - 力扣（LeetCode）

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
        fake = ListNode()
        fake.next = head
        cur = fake
        while cur.next and cur.next.next:
            temp = cur.next
            temp2 = cur.next.next.next
            cur.next = cur.next.next
            cur.next.next = temp
            cur.next.next.next = temp2
            cur = cur.next.next
        return fake.next

19. 删除链表的倒数第 N 个结点 - 力扣（LeetCode）

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
        fake = ListNode(0,head)
        slow = fake
        fast = fake
        for i in range(n+1):
            fast = fast.next
        while fast:
            fast = fast.next
            slow = slow.next
        slow.next = slow.next.next
        return fake.next

142. 环形链表 II - 力扣（LeetCode）

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

class Solution:
    def detectCycle(self, head: Optional[ListNode]) -> Optional[ListNode]:
        fast = head
        slow = head
        while fast and fast.next and fast.next.next:
            fast = fast.next.next
            slow = slow.next
            if fast == slow:
                index1 = fast
                index2 = head
                while index1 != index2:
                    index1 = index1.next
                    index2 = index2.next
                return index1
        return None