Example code to find the nth node from the end of a linked list using only one pass.

main.cpp

#include <iostream>
#include <assert.h>
 
namespace std { };
using namespace std;
 
struct node
{
   node* next;
   size_t data;
};
 
const node* find_nth_node_from_tail(const node* n, size_t i)
{
   const node* t = n;
 
   while (n != NULL)
   {
      n = n->next;
 
      if (i == 0)
      {
         t = t->next;
      }
      else
      {
         --i;
      }
   }
 
   return t;
}
 
const node* find_nth_node_from_tail_improved(const node* n, size_t i)
{
   const node* t = n;
 
   while (i-- > 0 && n != NULL)
   {
      n = n->next;
   }
 
   while (n != NULL)
   {
      n = n->next;
      t = t->next;
   }
 
   return t;
}
 
node* reverse_linked_list(node* head)
{
   if (head != NULL)
   {
      node* prev = NULL, * current = NULL, * next = NULL;
      current = head;

      while (current != NULL)
      {
         next = current->next;
         current->next = prev;
         prev = current;
         current = next;
      }

      head = prev;
   }

   return head;
}

int main(int argc, char* argv[])
{
   node list[8];
   list[0].data = 1;
   list[0].next = &list[1];
   list[1].data = 2;
   list[1].next = &list[2];
   list[2].data = 3;
   list[2].next = &list[3];
   list[3].data = 4;
   list[3].next = &list[4];
   list[4].data = 5;
   list[4].next = &list[5];
   list[5].data = 6;
   list[5].next = &list[6];
   list[6].data = 7;
   list[6].next = &list[7];
   list[7].data = 8;
   list[7].next = NULL;
 
   const node* result = find_nth_node_from_tail_improved(list, 5);
  
   assert(result->data == 4);
 
   result = reverse_linked_list(list);

   assert(result->data == 8);

   return 0;
}