7.4 Run times of our program for just four blocks are trivial. However, how about larger numbers of blocks? If the program of Figure 7.4 was extended to handle any number of blocks, its complexity would grow rapidly with the number of blocks. Fortunately, our program usually recognizes many hopeless alternatives quite early, so that large subsets of hopeless alternatives are not fully explored at all. Analyse where in the program the sources of combinatorial complexity occur and work out the order of complexity in the worst case.