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.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *removeNthFromEnd(ListNode *head, int n) 
    {
        if(head==NULL) return NULL;
        
        ListNode* p1=head;
        ListNode* p2=head;
        int count=1;
        while(count<=n) 
        {
            count++;
            p2=p2->next;
        }
        if(p2==NULL)
            return head->next;
            
        while(p2->next!=NULL)
        {
            p1=p1->next;
            p2=p2->next;
        }
        
        p1->next=p1->next->next;
        
        return head;
    }
};