[LintCode] 删除链表中倒数第n个节点

/**
 * 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
        ListNode* pre = head;
        ListNode* cur = head;
        for (int i = 0; i < n; i++)
            cur = cur -> next;
        if (!cur) {
            delete pre;
            return pre -> next;
        }
        while (cur -> next) {
            pre = pre -> next;
            cur = cur -> next;
        }
        delete pre -> next;
        pre -> next = pre -> next -> next;
        return head;
    }
};