代码随想录Day4 | LeetCode 24. 两两交换链表中的节点、LeetCode 19. 删除链表的倒数第 N 个结点、LeetCode 160. 相交链表

LeetCode 24. 两两交换链表中的节点

递归思想

# 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]:if not head or not head.next:return headpre = self.swapPairs(head.next.next)next = head.nexthead.next = prenext.next = headreturn next

LeetCode 25. K 个一组翻转链表

一道拓展

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:if not head:return headp1 = p2 = headfor _ in range(k):if not p2:return headp2 = p2.nextpre = self.reverseKGroup(p2, k)while p1 != p2:next = p1.nextp1.next = prepre = p1p1 = nextreturn pre

LeetCode 19. 删除链表的倒数第 N 个结点

双指针

# 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]:if not head:return headdummy = ListNode()dummy.next = headp1 = p2 = dummyfor _ in range(n):p2 = p2.nextwhile p2.next:p1 = p1.nextp2 = p2.nextp1.next = p1.next.nextreturn dummy.next

LeetCode 160. 相交链表

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = Noneclass Solution:def getIntersectionNode(self, headA: ListNode, headB: ListNode) -> Optional[ListNode]:p1, p2 = headA, headBwhile p1 != p2:p1 = p1.next if p1 else headBp2 = p2.next if p2 else headAreturn p1