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public class List extends Pos
{
public Pos front, last;
public Pos front()
{
return this;
}
public boolean isempty()
{
return (front() == null);
}
public List empty()
{
return null;
}
public Pos next(Pos p)
{
return p.succ;
}
public boolean bol(Pos p)
{
return (front() == p);
}
public boolean eol(Pos p)
{
return (this.last == p);
}
public List insert(Pos p, Elem el)
{
Pos q = new Pos();
q.value = el;
if(!(eol(p) || isempty()))
{
q.pred = p;
q.succ = p.succ;
p.succ.pred = q;
p.succ = q;
}
else
{
q.pred = p;
q.succ = null;
p.succ = q;
pred = q; // Last-Zeiger aendern
}
return this;
}
public List delete(Pos p)
{
Pos q;
if(!isempty())
{
if(eol(p))
{
if(p == this.front)
{
last = null;
p.succ = null;
}
else
{
q = this.front;
while(q.succ != p) q = q.succ;
last = q;
p.succ = null;
}
}
else
{
q = p.succ;
if(q == last) last = p;
p.succ = p.succ.succ;
}
}
return this;
}
}
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