LintCode-劍指Offer-(174)刪除鏈表中倒數第n個節點

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param head: The first node of linked list.
     * @param n: An integer.
     * @return: The head of linked list.
     */
    ListNode *removeNthFromEnd(ListNode *head, int n) {
        // write your code here

        if(head->next==NULL)//如果只有一個節點
            return NULL;
        ListNode* tmp=head;
        int count=0;
        while(tmp!=NULL){
            count++;
            tmp=tmp->next;
        }
        if(n==count)//如果要刪除的是頭結點
        {
            head=head->next;
            return head;
        }
        tmp=head;
        while(count>n+1){//否則找到節點，進行刪除
            tmp=tmp->next;
            count--;
        }
        tmp->next=tmp->next->next;
        return head;
    }
};