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
        ListNode *currentPre = head;
        ListNode *beforePre = NULL;
        ListNode *firstPre = NULL;
        ListNode *newPre = NULL;
        ListNode *lastPre = NULL;
        if(n==m)
            return head;
        for (int i=1; i <= n; i++) {
            
            if(i<m-1)
            {
                currentPre = currentPre->next;
            }
            else if(i == m-1 && m != 1)
            {
                firstPre = currentPre;
                lastPre = currentPre->next;
                currentPre = currentPre->next;
            }
            else if (i>=m&&i<=n) {
                newPre = currentPre->next;
                currentPre->next = beforePre;                
                beforePre = currentPre;
                currentPre = newPre;
                
            }           
            
        }
        if(m == 1)
        {
            head->next = newPre;
            return beforePre;
        }
        else {
            firstPre->next = beforePre;
            lastPre->next = newPre;
            return head;
        }
        
    }
    
};