linked_list_remove_from_end.cc

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode *ptr = new ListNode();
        ptr->next = head;
        ListNode *p = ptr;
        ListNode *q = ptr;
        
        for (int i = 0; i < n; i++)
            p = p->next;
        
        while (p->next) {
            p = p->next;
            q = q->next;
        }
        
        q->next = q->next->next;
        return ptr->next;
    }
};