leetcode:Remove Nth Node From End of List

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
//这道题比较简单，但是要想清楚当删除链表头节点，中间节点和尾节点三种情况
class Solution {
public:
ListNode *removeNthFromEnd(ListNode *head, int n) {
ListNode *kp=head;
ListNode *mp=head;
ListNode *pre=mp;
int step=0;
while(kp->next!=NULL && step<n-1 )
{
kp=kp->next;
step++;
}
while(kp->next!=NULL)
{
kp=kp->next;
pre=mp;
mp=mp->next;
}
if(pre==head && pre==mp)
{
head=pre->next;
pre->next=NULL;
delete pre;
}
else
{
pre->next=mp->next;
mp->next=NULL;
delete mp;
}

return head;
}
};