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) {}
 * };
 */
#include <cstddef>
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
        if ( head == nullptr )
        {
            return nullptr;
        }
        if ( m == n ){
            return head;
        }
        auto *res = new ListNode(0);
        ListNode *p = res;
        ListNode *temp = nullptr;
        ListNode *t = nullptr;
        bool first = true;
        res->next = head;
        int cur_index = 0;
        while ( head != nullptr )
        {
            cur_index ++;
            if ( cur_index < m)
            {
                p = head;
                head = head->next;

            }
            else if ( cur_index >= m && cur_index <= n )
            {   
                p->next = head;
                head = head->next;
                p->next->next = temp;
                temp = p->next;
                if ( first ){
                    t = temp;
                    first = false;
                }
            }
            else 
            {
                break;
            }
            
        }
        t->next = head;

	    return res->next;
    }
};