19. Remove Nth Node From End of List

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.

/**

 * Definition for singly-linked list.

 * struct ListNode {

 *     int val;

 *     ListNode *next;

 *     ListNode(int x) : val(x), next(NULL) {}

 * };

 */

class Solution {

public:

    ListNode* removeNthFromEnd(ListNode* head, int n) {

        ListNode* dummy = new ListNode(0);

        dummy->next = head;

        ListNode* slow = dummy;

        ListNode* fast = dummy;

        for (int i = 0; i < n; i++) {

            fast = fast->next;

        }

        while (fast != NULL && fast->next != NULL) {

            fast = fast->next;

            slow = slow->next;

        }

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

        return dummy->next;

    }

};