Vom Amazon-Stand entliehen:

ninja(int u, int v) {
if (v==0) return u;
return ninja(v, u%v);
}
//what does ninja do?
//hint: ninja terminates for every input

Und hier noch eine zweite:

ninja(x)
{
if (x==0) return 0;
if (x==1) return 1;

if (x==2) return 1; //ninja line
return ninja(x-1) + ninja(x-2);
}
//if you comment out the ninja line,
//how much more calls to ninja are
//made. express in terms of n