diff options
| -rw-r--r-- | challenge-118/james-smith/README.md | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/challenge-118/james-smith/README.md b/challenge-118/james-smith/README.md index 4bd537294d..ef42a1c173 100644 --- a/challenge-118/james-smith/README.md +++ b/challenge-118/james-smith/README.md @@ -315,7 +315,6 @@ The numbers 6, 10, 15 and 17 come from looking at the grid above.... -10 ... ... ... -6 ... -17 ... -15 ... ``` -We then have an optimized version of the walk code: The array looks something like: ``` @@ -332,30 +331,32 @@ The array looks something like: ] ``` -The walk sub then becomes the simpler: +We then have an optimized version of the walk code, and subroutine then becomes the *simpler*: ```perl sub walk_trans { - my( $t, $seen, $rt ) = @_; ## Current square, visited squares, current route - return if $seen & 1 << $t; ## Return if we've already been to this square. - $seen |= 1 << $t; ## Mark that we have been in this square. - $rt .= chr $t; ## Add this square to our route. - return ($best_rt,$best_len) = ($rt,-1+length $rt) if ($seen & $sol) == $sol; - ## If we've found all the treasure - ## Update the best route (and it's length) - ## and return; - return if $best_len <= length $rt; - ## If our route is longer than the best route - ## return; - walk_trans( $_, $seen, $rt ) foreach @{$trans->[$t]}; - ## Try all knight move squares from the current - ## square. + my( $t, $seen, $rt ) = @_; ## Current square, visited squares, current route. + + return if $seen & 1 << $t; ## Return if we've already been to this square. + + $seen |= 1 << $t; ## Mark that we have been in this square. + + $rt .= chr $t; ## Add this square to our route. + + return ($best_rt,$best_len) ## If we've found all the treasure update the best + = ($rt,-1+length $rt) ## route (and it's length) and return + if ($seen & $sol) == $sol; + + return if $best_len <= length $rt; ## If longer than the best route return + + walk_trans( $_, $seen, $rt ) ## Try all knight move squares from the current + foreach @{$trans->[$t]}; ## square. } ``` -The eight lines of `if`s go back to a single foreach loop. +The eight lines of `if`s go back to a single foreach loop, but this time we do not need the `if`s. -As well as removing the ifs we have a "side-effect" where we no longer need to label squares by their x&y co-ordinates but just by their index 0..63 which also gains us a little speed. +As well as removing the ifs we have a "side-effect" where we no longer need to label squares by their `x`&`y` co-ordinates but just by their index `0`..`63` which also gains us some additional speed {we no longer have to compute `$t` from `$x` & `$y`, and we need to pass one less parameter} The time is now down to approximately 10 seconds. |