Inductive Step: Show that P(k) is true where k > 1, that is to put k-1 pieces of jigsaw
together requires k-1 steps.
To put together k pieces, the final step involves putting together two blocks of jigsaw.
Suppose one jigsaw block consists of r pieces and the the other one consists of k − r
pieces. Obviously, r < k and k − r < k. By the induction hypothesis, we know that
P(r) and P(k −r) are true, that is we can put together r prices jigsaws and k-r pieces of
jigsaw using r-1 and k-r-1 steps respectively. Hence the total number of steps required
to put together k pieces of jigsaw is (r − 1) + (k − r − 1) + 1 = k − 1