标签：for 注意 res lis sel linked not 添加 link
反转一个单链表。
示例:
输入: 1->2->3->4->5->NULL 输出: 5->4->3->2->1->NULL
用一个变量记录pre，一个变量记录next,不断更新current.next = pre
注意更新 cur 和 pre 的位置， 否则有可能出现溢出
python
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def reverseList(self, head: ListNode) -> ListNode: if not head:return None prev=None cur=head while cur: cur.next,prev,cur=prev,cur,cur.next return prev
Java
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ class Solution { public ListNode reverseList(ListNode head) { ListNode pre=null,cur=head; while(cur!=null){ ListNode next=cur.next; cur.next=pre; pre=cur; cur=next; } return pre; } }
单链表也是递归结构，因此，也可以使用递归
c++
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ //普通递归 class Solution { public: ListNode* reverseList(ListNode* head) { ListNode* tail=nullptr; return reverseRecursive(head,tail); } ListNode* reverseRecursive(ListNode* head,ListNode*&tail){ if(head==nullptr){ tail=nullptr; return head; } if(head->next==nullptr){ tail=head; return head; } auto h=reverseRecursive(head->next,tail); if(tail!=nullptr){ tail->next=head; tail=head; head->next=nullptr; } return h; } };
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ //（类似）尾递归 class Solution { public: ListNode* reverseList(ListNode* head) { if(head==nullptr)return head; return revreseRecursive(nullptr,head,head->next); } ListNode* revreseRecursive(ListNode* prev,ListNode* head,ListNode* next){ if(next==nullptr)return head; auto n=next->next; next->next=head; head->next=prev; return revreseRecursive(head,next,n); } };
python
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def reverseList(self, head: ListNode) -> ListNode: if not head or not head.next:return head ans=self.reverseList(head.next) head.next.next=head head.next=None return ans
标签：for 注意 res lis sel linked not 添加 link
原文地址：https://www.cnblogs.com/xxxsans/p/12949012.html
