Leetcode--19. Remove Nth Node From End of List

题目：Given a linked list, remove the nth node from the end of list and return its head.

For example,

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:

Given n will always be valid.

Try to do this in one pass.

C++代码如下：

ListNode* removeNthFromEnd(ListNode* head, int n) {
if (head == NULL)
return NULL;

int k = 1;
ListNode *p = head, *q = head, *qPre = NULL;
while (k < n)
{
p = p->next;
k++;
}
while (p->next != NULL)
{
qPre = q;
q = q->next;
p = p->next;
}
if (qPre == NULL)
{
head = q->next;
delete q;
}
else
{
qPre->next = q->next;
q = NULL;
delete q;
}
return head;
}