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
        if(!head || !head->next || n-m < 1) return head;

        ListNode LL = ListNode(-1);
        ListNode* PreHead = &LL;
        PreHead->next = head;
        ListNode* rePre = PreHead;
        ListNode* reNext = head->next;

        for(int i=1; i< n; i++){
            if(i < m) rePre = rePre->next;
            reNext = reNext->next;
        }
        ListNode* Phead = rePre->next,*temp = nullptr,*Pre = reNext;

        for (int i=0; i<n-m + 1; i++) {
            temp = Phead->next;
            Phead->next= Pre;
            Pre = Phead;
            Phead = temp;
        }   
        rePre->next = Pre; 

        return PreHead->next;

    

    }
};