///////    File :  List.C    ///////
#include <iostream.h>
#include "List.h"

List::~List() {   free();  }

void List::free() // private method
{    ListCell* n, *p = head;
     while (p)
     {   n = p->next;
         delete p;
         p=n;
     }
}

int List::shorten(int n)
{    while (n-- && head)
     {   ListCell* tmp=head;
         head = head->next;
         delete(tmp);
     }
     return(0);
}

int List::remove(char c)
{     ListCell *tmp, *p = head;
      int count = 0;
      if ( p == NULL ) return(count);
      while (p->next)      // treat all but head cell
      {  if ((p->next)->item == c)
         {   count++;
             tmp = p->next;
             p->next = tmp->next;
             delete(tmp); // free up store
         }
         else
                p = p->next;
      }
      if( head->item == c ) // treat head cell
      {  tmp = head;
         head = head->next;
         delete(tmp);
         count++;
      }
      return(count);        // number of items removed
}

int List::put_on(char c)
{     ListCell* tmp = new ListCell(c,head);
      if ( tmp )
      {  head = tmp;
         return(0);
      }
      else return(-1); // failed
}

// insert after entry e
int List::insert(char c, ListCell* e)
{     ListCell* tmp = new ListCell(c,e->next);
      if ( tmp )
      {  e->next = tmp;
         return(0);
      }
      else return(-1); // failed
}

ListCell* List::last()
{     ListCell* p = head;
      while( p && p->next ) p =  p->next; 
      return(p);
}

ListCell* List::find(char c)
{   for( ListCell* p = head; p ; p = p->next )
       if( p->item == c )
           return(p);
    return(NULL);  // c not on list
}

int List::substitute(char r, char s)
{     ListCell* p = find(s);
      if( p == NULL ) return(-1);     // s not on list
      p->item = r;
      return(0);
}

// display from p to end
void List::display(ListCell* p)
{   cout << "(";
    while ( p )
    {    cout << p->item;
         if ( p = p->next ) cout << " ";
    }
    cout << ")\n";
}