題目：
Find the middle node of a linked list.
代碼：
public:
/**
* @param head: the head of linked list.
* @return: a middle node of the linked list
*/
ListNode *middleNode(ListNode *head) {
// Write your code here
if (head == NULL)
return NULL;
int cnt = 0;
ListNode *p = head;
while (p != NULL) {
cnt ++;
p = p->next;
}
cnt = (cnt + 1) / 2;
while (head != NULL) {
if (cnt == 1)
return head;
cnt --;
head = head->next;
}
}
};
