19.Remove Nth Node From End of List

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)
    {
        int size = 0;
        if (n <= 0 || !head)
            return head;

        ListNode *list1 = head, *list2 = head;
        int i = 0;
        for (i = 0; i < n; i++)
        {
            if (!list2)
                break;
            list2 = list2->next;
        }

        if (i != n)      // n大于链表长度
            return head;

        if (!list2)
        {
            ListNode* temp = head;
            head = head->next;
            delete temp;
            return head;
        }

        while (list2->next)
        {
            list1 = list1->next;
            list2 = list2->next;
        }

        ListNode* temp = list1->next;
        list1->next = temp->next;
        delete temp;

        return head;
    }
};