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) {
        // write code here
        ListNode* dummy = new ListNode(0);  //创建虚拟链表
        ListNode* dummy_head = dummy; //创建虚拟链表头
        ListNode* pre = nullptr;
        ListNode* temp = nullptr;
        for(int i=1;i<m;i++)  //遍历前m-1个，将head赋给虚拟链表
        {
            dummy_head->next = head;  //虚拟链表头指向head
            dummy_head = dummy_head->next;  //创建虚拟链表头移到虚拟链表头next
            head = head->next;  //head链表头移到head链表头next
        }
        for(int i =m;i<=n;i++) //遍历m到n数值，将其翻转到pre
        {
            temp = head->next;  //保存head的next
            head->next = pre;  //head指向prepre
            pre = head;   //pre链表头移到head
            head =temp;  //head移到保存好的head的next
        }
        for(int i =m;i<=n;i++) //遍历m到n数值，将翻转得到的pre赋给虚拟链表
        {
            dummy_head->next =pre;  
            dummy_head = dummy_head->next;
            pre = pre->next;
        }
        dummy_head->next =head;  //剩下的直接赋给虚拟链表
        return dummy->next;
    }
};