题解 | #链表内指定区间反转#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * @param head ListNode类 
     * @param m int整型 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode* reverseBetween(ListNode* head, int m, int n) {
       ListNode* p1 = head;
       ListNode* p2 = nullptr;
       ListNode* preverse = nullptr;
        //头部插入一个结点
        ListNode* newnode = new ListNode(0); 
        newnode->next = p1;
        p1 = newnode;
        head = p1;
        //尾部插入一个结点
        while(p1->next != nullptr)
        {
            p1 = p1->next;
        }
        newnode = new ListNode(0);
        p1->next = newnode; 
        p1 = head;
        m++;n++;
        for(int i=1; i < m-1; i++)
        {
            p1 = p1->next;
        }
        p2 = p1;
        p1 = p1->next;
        for(int i=0; i<n-m+1; i++)
        {
            newnode = new ListNode(p1->val);
            newnode->next = preverse;
            preverse = newnode;
            p1 = p1->next; 
        }
        p2->next = preverse;
        while(preverse->next != nullptr)
        {
            preverse = preverse->next;
        }
        preverse->next = p1; 

         p1 = head;
         while(p1->next->next != nullptr)
         {
            p1 = p1->next;
         }   
        p1->next = nullptr;
	  
        return head->next;        
    }
};