翻转链表

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) 
    {
        if (pHead == nullptr || pHead -> next == nullptr)
            return pHead;
        ListNode* currentNode = pHead;
        ListNode* preNode = nullptr;
        while (currentNode -> next != nullptr)
        {
            ListNode* nextNode = currentNode -> next;
            currentNode -> next = preNode;
            preNode = currentNode;
            currentNode = nextNode;
        }
        currentNode -> next = preNode;
        return currentNode;
        
        
    }
};