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| -rw-r--r-- | sicp.org | 44 |
1 files changed, 44 insertions, 0 deletions
@@ -574,3 +574,47 @@ Now (using =cons= instead of =list=) it is: scheme@(guile-user)> (make-branch 5 (make-mobile (make-branch 3 50) (make-branch 3 50))) $60 = (5 (3 . 50) 3 . 50) #+END_SRC +*** 43 + I'll measure the the time taken for function ~queens~ to complete + by calculating the number of times ~queen-cols~ gets called. + + First, I'm going to see how many times ~queen-cols~ gets called + for the original version of ~queens~ with ~board-size=8~ + + #+begin_example + board-size = 8 ; k = 8 -> 1 * (queen-cols 7) + ; k = 7 -> 1 * (queen-cols 6) + ; k = 6 -> 1 * (queen-cols 5) + ; k = 5 -> 1 * (queen-cols 4) + ; k = 4 -> 1 * (queen-cols 3) + ; k = 3 -> 1 * (queen-cols 2) + ; k = 2 -> 1 * (queen-cols 1) + ; k = 1 -> 1 * (queen-cols 0) + ; k = 0 -> 0 + #+end_example + + ~queen-cols~ gets called 8 times when ~board-size~ is 8 + + To generalize it ~queen-cols~ gets called B times when the + ~board-size~ is B. + + Next, I'm going to see how many times ~queen-cols~ gets called for + Louis Reasoner's version of the of ~queens~ + + #+begin_example + board-size = 8 ; k = 8 -> 8 * (queen-cols 7) + ; k = 7 -> 8 * (queen-cols 6) + ; k = 6 -> 8 * (queen-cols 5) + ; k = 5 -> 8 * (queen-cols 4) + ; k = 4 -> 8 * (queen-cols 3) + ; k = 3 -> 8 * (queen-cols 2) + ; k = 2 -> 8 * (queen-cols 1) + ; k = 1 -> 8 * (queen-cols 0) + ; k = 0 -> 0 + #+end_example + + Here, the ~queen-cols~ is getting called ~8^8~ times or ~B^B~ + times when the ~board-size is B. + + From above, if the original version of ~queens~ took time ~T~, + then Louis's version will take ~T^T~ to finish. |