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>
#include <functional>
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
        int i = 1;
        
        ListNode* first = head;
        ListNode* left = first;
        ListNode* second = nullptr;
        while (i < m) {
            i++;
            left = first;
            first = first->next;
        }
        int flag = 0;
        if (i == 1) {
            flag = 1;
            left = new ListNode(0);
            left->next = first;
        }
        // left = first->next;
        while(i < n){
            second = first->next;
            first->next = second->next;
            second->next = left->next;
            left->next = second;
            i++;
        }
        if (flag == 1) {
            head = left->next;
        }

        return head;
    }
};