Remove Nth Node From End of List

题目：

Given a linked list, remove the nth node from the end of list and return its head.

The minimum number of nodes in list is n.

Example Given linked list: 1->2->3->4->5->null, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5->null.

分析：

从这个题目中就学到一件事，从dummy开始做，一切都好，从head开始做，什么都完蛋！

解法：

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 == NULL) {
            return NULL;
        }

        ListNode dummy(-1);
        dummy.next = head;

        ListNode* slow = &dummy;
        ListNode* fast = &dummy;

        for (int i = 0; i < n; i++) {
            fast = fast->next;
        }

        while (fast->next != NULL) {
            slow = slow->next;
            fast = fast->next;
        }

        slow->next = slow->next->next;

        return dummy.next;
    }
};