1.反转链表
描述：将链表（头结点要存放数据）反转，如输入的是{1,2,3,4}，反转之后得到{4,3,2,1}
struct ListNode {
int val;
struct ListNode *next;
};
struct ListNode* ReverseList(struct ListNode* pHead ) {
// write code here
struct ListNode *p=NULL;
struct ListNode *temp=NULL;
while(pHead!=NULL){
temp=pHead->next;
pHead->next =p;
p=pHead;
pHead = temp;
}
pHead = p;
return pHead;
}