YXC题解

class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int left, int right) {
        auto dummy = new ListNode(-1); //虚拟头节点（一般头结点可变或可不变的情况，我们这时可创建一个虚拟头结点）
        dummy->next = head; 
        auto a = dummy;
        for (int i = 0; i < left - 1; i ++) { //从dummy走left-1步，确定a的位置，a是left前的一个位置
            a = a->next;
        }
        auto b = a->next, c = b->next;
        for (int i = 0; i < right - left; i ++) { //
            auto d = c->next;
            c->next = b;
            b = c, c = d;
        }
        a->next->next = c;
        a->next = b;
        return dummy->next; //返回的是真实的头结点
    }
};