Leetcode 206——反转字符串

分递归和非递归，代码如下：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) 
    {
        //ListNode *pResult = reverseCoreRecursively(head);
        ListNode *pResult = reverseCoreLoop(head);
        return pResult;
    }
    
    ListNode* reverseCoreLoop(ListNode *pNode)
    {
        if (pNode == nullptr)
            return nullptr;
        
        ListNode *pNewHead = pNode;
        pNode = pNode->next;
        pNewHead->next = nullptr;
        while (pNode != nullptr)
        {
            ListNode *pTempNewHeadNode = pNode;            
            pNode = pNode->next;
            pTempNewHeadNode->next = pNewHead;
            pNewHead = pTempNewHeadNode;
        }
        
        return pNewHead;
    }
    
    
    
    ListNode* reverseCoreRecursively(ListNode* pNode)
    {
        if (pNode == nullptr)
            return nullptr;
        
        if (pNode->next == nullptr)    
            return pNode;
        
        ListNode *pCurNode = reverseCoreRecursively(pNode->next);
        ListNode *pTempNode = pCurNode;
        while(pTempNode->next != nullptr)
        {
            pTempNode = pTempNode->next;
        }
        pTempNode->next = pNode;
        pNode->next = nullptr;
    
        return pCurNode;
    }
};

感觉递归的代码还可以优化