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.

/**
* 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) {
ListNode* result=new ListNode(0);
result->next=head;
int length=0;
ListNode* p=result;
while(p->next)
{
length++;
p=p->next;
}
p=result;
if(length==0||length<n) return result->next;
int point=length-n+1;
int i=1;
while(p->next)
{
if(i==point)
{
p->next=p->next->next;
break;
}
p=p->next;
i++;
}
return result->next;
}
};