Reverse Linked List I

Question Solution

/**

 * 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) {

        if(head==NULL || head->next == NULL){

            return head;

        }

        ListNode* firstNode = head;

        ListNode* preCurNode = head;

        ListNode* curNode = head->next;//maybe null

        while(curNode){

            preCurNode->next = curNode->next;

            curNode->next = firstNode;

            firstNode=curNode;

            curNode =preCurNode->next;  

        }

        return firstNode;

    }

};

/**

 * 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) {

        if(head==NULL||head->next==NULL||m==n)

            return head;

        ListNode* firstNode = head;

        ListNode* preCurNode = head;

        ListNode* curNode = head->next;//maybe null

        ListNode* lastNode= head;

        int flag=;

        int m_flag=flag;

        if(m==)

        {

            while(flag<n)

            {

                preCurNode->next = curNode->next;

                curNode->next = firstNode;

                firstNode=curNode;

                curNode =preCurNode->next;

                flag++;

            }

           return firstNode;

        }

        else

        {

            while(flag<n)

            {

              if(flag<m)

              {

                  lastNode=firstNode;

                 firstNode=firstNode->next;

                 preCurNode =preCurNode->next;

                 curNode =curNode->next;

                 flag++;

              }

              else

              {

                preCurNode->next = curNode->next;

                curNode->next = firstNode;

                firstNode=curNode;

                curNode =preCurNode->next;

                lastNode->next=firstNode;

                flag++;

               }

             }

         return head;

        }

    }

};