leetcode——链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode *newHead=NULL;
        while(head){
            ListNode *next=head->next;
            head->next=newHead;
            newHead=head;
            head=next;
        }
        return newHead;
    }
};

# 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:
        newHead=None
        while head!=None:
            nxt=head.next
            head.next=newHead
            newHead=head
            head=nxt
        return newHead

/**
 * 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 newHead=null;
        while(head!=null){
            ListNode next=head.next;
            head.next=newHead;
            newHead=head;
            head=next;
        }
        return newHead;
    }
}

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int m, int n) {
        ListNode* sta=head;
        int len=n-m+1;
        ListNode* pre=NULL;
        while(--m&&head){
            pre=head;
            head=head->next;
        }
        ListNode* e=head;
        ListNode* newHead=NULL;
        while(len--&&head){
            ListNode* next=head->next;
            head->next=newHead;
            newHead=head;
            head=next;
        }
        e->next=head;
        if(pre)
            pre->next=newHead;
        else 
            sta=newHead;
        return sta;
    }
};