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

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.

Runtime: 9 ms

class Solution{
public:
ListNode *removeNthFromEnd(ListNode *head, int n)
{
if (head == NULL)
return NULL;

ListNode*p1 = head;
ListNode*p2 = head;
ListNode*pre = NULL;
while (n-1 != 0)
{
p1 = p1->next;
n--;
}

while (p1->next)
{
pre = p2;
p2 = p2->next;
p1 = p1->next;
}

if (p2 == head)
head = head->next;
else
{
pre->next = p2->next;
delete p2;
}
return head;
}
};