July 2007 - quiz@common-lisp.net - mailman3.common-lisp.net

[quiz] [QUIZ 5b & 5e] Date differences, and betting (Larry Clapp) [spoiler]
by Chiao-Lun Cheng 25 Jul '07

25 Jul '07

My solution to the betting problem: (defun bet (total maxgames score1 score2 &optional err-check-off) (let ((thresh (floor (/ maxgames 2)))) (unless err-check-off (cond ((evenp maxgames) (error "Only odd numbers of total games allowed")) ((or (> score1 thresh) (> score2 thresh)) (error "Scores must be below half the total number of games")) ((or (< maxgames 0) (< score1 0) (< score2 0)) (error "maxgame, score1 and score2 must not be negative")))) (cond ((or (= score1 (1+ thresh)) (= score2 (1+ thresh))) 0) ((and (= score1 thresh) (= score2 thresh)) total) (t (/ (+ (bet total maxgames (1+ score1) score2 t) (bet total maxgames score1 (1+ score2) t)) 2))))) Given the you bet $a this round, and $b / $c next round, then a win-loss or a loss-win must put you back at the same value, meaning that a - b = -a +c and therefore a = (b+c)/2 That's the recursion that took me some time to realize. Otherwise the coding is straightforward. -- ******************************************* Chiao-Lun Cheng Van Voorhis Group Department of Chemistry, Room 6-234 Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge, MA 02139-4307 Email : chiao(a)mit.edu Tel : +1 (617) 253-1539 Website : http://zeno.unixboxen.net *******************************************

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[quiz] [QUIZ 5b & 5e] Date differences, and betting
by Larry Clapp 24 Jul '07

24 Jul '07

Beginner: Adapted from Perl Quiz #2: [ http://perl.plover.com/~alias/list.cgi?mss:11:200210:ccbcblpijjjcnhnkabep ] Write a function, days-diff, to compute the time difference, in days, between two dates. The dates will be strings in the format Wed Oct 16 2002 For example: (days-diff "Wed Oct 16 2002" "Wed Oct 23 2002") => 7 (days-diff "Wed Oct 16 2002" "Tue Oct 16 2001") => -365 Error checking: at minimum, signal an error if either value is unparsable or internally inconsistent (e.g. if 10/16/2002 is not, in fact, a Wednesday). More advanced users can establish useful restarts. Dependencies on your Lisp's time functions are okay. Expert: Adapted from Expert Perl Quiz #2: [ http://perl.plover.com/~alias/list.cgi?mss:12:200210:mflioldnngfgmfnlfljf ] The local high school baseball team, the Kent Pitman High School Phoenixes, will be playing a series of games against their rivals, the Kenny Tilton Memorial High School Growlin' Fungus. The series lasts at most five games, and ends when one team has won three games. You want to bet $80 on the Phoenixes to win the series, but your bookie will only take bets on individual games. (The bookie pays even money on all bets.) A mathematically-inclined friend solves the problem for you, giving you the following instructions: Bet $30 on each of the first two games. Bet $20 on the third game if either team has won both of the first two games, $40 otherwise. Bet $40 on the fourth game, if there is one. Bet $80 on the fifth game, if there is one. At the end of the series, you will be ahead by exactly $80 if the Phoenixes have won the series, and behind by exactly $80 if the Growlin' Fungus have won. We could summarize the instructions in a table like this: If the game score is: 0 to 0, bet $30 1 to 0, bet 30 1 to 1, bet 40 2 to 0, bet 20 2 to 1, bet 40 2 to 2, bet 80 Write a function which calculates the appropriate bet for any such contest, given the total amount you want to risk on the series, the length of the series, and the current game score. For example, (bet 80 5 2 1) => 40 because if you want to risk $80 on a 5-game series, and one team is presently ahead 2 games to 1, you should bet $40. Similarly (bet 1000 7 2 1) => 375 (That is, if you're trying to bet $1000 on the current [circa 10/2002] World Series baseball match, you need to bet $375 on the outcome of tonight's game. If you started with $1000, and followed this function's advice, you'd have $625 left if you had been betting on the Giants and $1375 if you had been betting on the Angels. For people living in places where the World Series is irrelevant: the match is a best-four-of-seven series of games; at present, the Anaheim Angels are beating the San Francisco Giants two games to one, with the fourth game scheduled for tonight.) Error checking: at minimum, signal an error if any of the parameters are invalid or internally inconsistent (e.g. negatives, length of series is less than number of games played so far, etc). More advanced users can establish useful restarts.

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[quiz] Anybody there?
by Ivan Salazar 12 Jul '07

12 Jul '07

It sounds interesting. I'd like to join in, even if I'm a real newbie. Have you got any ideas?

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[quiz] call for quizzes, and [QUIZ 4] centering
by Larry Clapp 12 Jul '07

12 Jul '07

I think there's interest in this list, I just think the guy that started it (Marco Baringer) ran out of or overestimated his free time. If you have a puzzle or quiz, feel free to post it to the list. Heck, if you have some (short) Lisp code that's just not working and you don't know why, post it to the list. [ /me Googles ... ] This list started as an imitation of the Perl quiz of the week, so I'll shamelessly copy their first quiz (see below). I'd also like to ask everyone to take a moment and re-read the rules of the game as posted here[1]. In particular: no solutions for 48 hours; if you post one after that, include "[SPOILER]" in the subject. I'll add to that: If you reply to a SPOILER thread and cut out the solution, you can remove SPOILER from the subject (or maybe change it to UNSPOILED just for fun :). Also, the Perl quiz site has the following Q&A (paraphrased): Q: Where to I send my answer? A: Don't feel obligated to send it anywhere. The point of solving the puzzle is to have solved it. I'm not Marco, of course, so feel free to ignore me. :) Anyway, the quiz: Write a function, 'center', whose argument is a list of strings, which will be lines of text. 'center' should insert spaces at the beginning of the lines of text so that if they were printed, the text would be centered, and return the modified lines. For example, (center "This" "is" "a test of the" "center function") should return the list: (" This" " is" " a test of the" "center function") because if these lines were printed, they would look like: This is a test of the center function -- Larry [1] http://common-lisp.net/project/quiz/

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[quiz] XKCD Appetizers Solution
by Chiao-Lun Cheng 11 Jul '07

11 Jul '07

I've pasted a brute force solution that uses Peter Norvig's tree-search function at http://paste.lisp.org/display/44376 -- ******************************************* Chiao-Lun Cheng Van Voorhis Group Department of Chemistry, Room 6-234 Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge, MA 02139-4307 Email : chiao(a)mit.edu Tel : +1 (617) 253-1539 Website : http://zeno.unixboxen.net *******************************************

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[quiz] [QUIZ 3] reader macro
by Larry Clapp 11 Jul '07

11 Jul '07

Okay, here's my 2 cent quiz: Define a reader macro that reads strings but treats backslashes as normal characters, except if you escape the string terminator. This should work sort of like Perl's single quote string syntax: Perl: $pattern = '\w \s'; # five characters Lisp: (let ((pattern #"\w \s")) ; five characters ...) as opposed to (let ((pattern "\\w \\s")) ; five characters ...) but this works: (let ((pattern #"\w \" \s")) ; seven characters ...) The #" syntax is just to give you an idea of what I want; you can use whatever macro character(s) you like. Send answers to the list, preferably with at least one working test case displayed, e.g. something like cl-user> #"\w \" \s" "\\w \" \\s" cl-user> -- L (Yes, this is similar to a previous quiz. Sue me.)

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[quiz] Anybody there?
by Carl 07 Jul '07

07 Jul '07

Is the CL-Quiz/mailing list still active? The archive doesn't have any articles more recent than November '06. I'm just getting started in CL and thought this might be a good resource for practice and learning. Carl.

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