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) {
        // write code here
        struct ListNode* ans = new ListNode(0);
        ans->next = head;
        ListNode *p = head, *q = ans, *l = head, *j = ans, *k = head;
        if (m == n) {
            return head;
        }
        for (int i = 0; i < m-1; i++) {
            q = p;
            p = p->next;
        }
        j = q;//区间前一位数
        for (int i = 0; i <= n-m; i++) {
            q = q->next;
        }
        k = q->next;//区间后一位数
        j->next = q;
        q = p->next;
        l = q->next;
        p->next = k;
        for(int i = 0; i < n-m-1; i++)
        {   
            q->next = p;
            p = q;
            q = l;
            l = l->next;
        }
        q->next = p;
        return ans->next;
    }
};