题解 | #链表内指定区间反转#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */

class Solution {
public:
    /**
     * 
     * @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(0);
        dummy.next = head;

        ListNode* pm = nullptr;
        ListNode* pn = nullptr;
        int i = 0;
        for (auto ptr=&dummy; ptr; i++) {
            if (m-1 == i) {
                pm = ptr;
            } else if (n == i) {
                auto nxtPtr = ptr->next;
                ptr->next = nullptr;
                auto tmp2 = pm->next;
                pm->next = reverseLink(pm->next);
                tmp2->next = nxtPtr;
                break;
            }

            ptr = ptr->next;
        }

        return dummy.next;
    }

    // 普通链表反转
    ListNode* reverseLink(ListNode* head) {
        ListNode* pre = nullptr;
        for (auto ptr=head; ptr; ) {
            auto nxt = ptr->next;
            ptr->next = pre;
            pre = ptr;
            ptr = nxt;
        }

        return pre;
    }
};