Suppose l is a list and p, q, and r are positions. as a function of n, the length of list l, determine how many times the functions first, end, and next are executed by the following program. p : = first(l); while p < > end(l) do begin q : = p; while q < > end(l) do begin q : = next(q, l); r : = first(l); while r < > q do r : = next(r, l) end; p : = next(p, l) end;