LCR 141. 训练计划 III - 力扣（LeetCode）

非递归

class Solution {
public:
    ListNode* trainningPlan(ListNode* head) {
        if(head != nullptr && head->next != nullptr)
        {
            ListNode* former = nullptr;
            ListNode* mid = head;
            ListNode* laster = nullptr;
            while(mid != nullptr)
            {
                laster = mid->next;
                mid->next = former;
                former = mid;
                mid = laster;
            }

            return former;
        }
       else
       {
            return head;
       } 
        
    }
};