Remove Nth Node From End of List. Given a linked list, remove the nth node from the end of list and return its head.

removeNthFromEnd.cc

/**
 * 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) {
        if(head == NULL)
            return NULL;
        ListNode guard(0);
        guard.next = head;
        // find the n-1th node from the end
        ListNode * p = &guard;
        ListNode * pp = &guard;
        for(int i = 0; i<n; ++i)
        {
            pp = pp->next;
            if(pp == NULL)
                return head;
        }
        while(pp->next)
        {
            pp = pp->next;
            p = p->next;
        }
        // remove p->next
        ListNode * temp = p->next;
        p->next = temp->next;
        delete temp;
        return guard.next;
    }
};