Remove Nth Node From End of List

Use two pointers and the first pointer move forwards n steps first.

 

/**
 * 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) {
    // IMPORTANT: Please reset any member data you declared, as
    // the same Solution instance will be reused for each test case.
    ListNode *dummy = new ListNode(0), *first = dummy, *second = dummy, *last = NULL, *res = NULL;
    dummy->next = head;
    for (int i = 0; i < n; ++i)
      first = first->next;
    while (first != NULL) {
      first = first->next;
      last = second;
      second = second->next;
    }
    last->next = second->next;
    delete second;
    res = dummy->next;
    delete dummy;
    return res;
  }
};