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反转链表

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输入一个链表，反转链表后，输出新链表的表头。

先保存子节点。

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/*
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;
        }
        else
        {
            ListNode *last = pHead;
            ListNode *current = pHead->next;
            ListNode *next = current->next;
            last->next = nullptr;
            current->next = last;
            while (next != nullptr)
            {
                last = current;
                current = next;
                next = next->next;
                current->next = last;
            }
            return current;
        }
    }
};