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) {
        if (head == nullptr) return head;
        auto pre = new ListNode(-1);
        auto new_head = pre;
        pre->next = head;
        auto start = head;  // 默认至少有一个，所以直接将start指向head
        for (auto i = 1; i < m; ++i){
          pre  = pre->next;
          start = start->next;
        }

        for ( auto i = 0; i < n-m; ++i) { // 默认从指定的m开始，设置为start，此时只需要n-m个调换就可以啦
          auto temp = start->next;
          start->next = temp->next;
          temp->next = pre->next;
          pre->next = temp;
        }

        auto ret = new_head->next; 
        delete new_head;// 将开始申请的临时头结点删除掉
        return ret;
    }
};