19. Remove Nth Node From End of List

19. Remove Nth Node From End of List
Difficulty: Easy

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.

给定一个链表，移除从链表结尾起的第n个结点，返回头结点。

struct ListNode {
    int val;
    struct ListNode *next;
};

struct ListNode* removeNthFromEnd(struct ListNode* head,int n)  {
    int m,listlen=0;
    struct ListNode* node;

    if(head==NULL)
        return head;

    node=head;
    while(node!=NULL)    //链表长度
    {
        listlen++;
        node=node->next;
    }
    m=listlen-n+1;    //移除链表起始的第m个
    if(m==1)
    {
        return head->next;
    }
    node=head;
    while(m>2)
    {
        node=node->next;
        m--;
    }
    node->next=node->next->next;
    return head;
}