Comments on: Quick Java Puzzler http://www.symphonious.net/2006/09/14/quick-java-puzzler/ Living in a state of accord. Fri, 09 Jan 2009 21:24:49 +0000 http://wordpress.org/?v=2.7 hourly 1 By: Milo http://www.symphonious.net/2006/09/14/quick-java-puzzler/comment-page-1/#comment-32138 Milo Thu, 14 Sep 2006 07:02:38 +0000 http://www.symphonious.net/2006/09/14/quick-java-puzzler/#comment-32138 Gah, hit submit while checking that post. min is -4 not -3. Gah, hit submit while checking that post. min is -4 not -3.

]]> By: Milo http://www.symphonious.net/2006/09/14/quick-java-puzzler/comment-page-1/#comment-32137 Milo Thu, 14 Sep 2006 06:59:59 +0000 http://www.symphonious.net/2006/09/14/quick-java-puzzler/#comment-32137 And for the nerd in me, it took me ages to understand twos-compliment so i love any chance to explain what's going on, humour me if you will: Say we have a number system with only 3 bits using twos-compliment. max number you get is 3, min is -3. the bit pattern for each number is: 000 0 001 1 010 2 011 3 100 -4 101 -3 110 -2 111 -1 two's complement flips the sign on a number by inverting the bit pattern and then adding one. For example, 2 is 010. flip the bits it becomes 101, add one you get 110, which as the table shows is -2. To show the original problem with an example, -4 is 100. flip the bits and you get 011, add 1 and voila, you get 100. The other cool (i really am a geek) case is negating 0. 000 flips to 111, we add 1 and we get 1000, but since we only have 3 bits, the leading 1 is lost and we end up with 000. So with twos-complements there are always 2 numbers that when negated will equal themself: 0 and the min. And for the nerd in me, it took me ages to understand twos-compliment so i love any chance to explain what’s going on, humour me if you will:

Say we have a number system with only 3 bits using twos-compliment. max number you get is 3, min is -3. the bit pattern for each number is:

000 0
001 1
010 2
011 3
100 -4
101 -3
110 -2
111 -1

two’s complement flips the sign on a number by inverting the bit pattern and then adding one. For example, 2 is 010. flip the bits it becomes 101, add one you get 110, which as the table shows is -2. To show the original problem with an example, -4 is 100. flip the bits and you get 011, add 1 and voila, you get 100.

The other cool (i really am a geek) case is negating 0. 000 flips to 111, we add 1 and we get 1000, but since we only have 3 bits, the leading 1 is lost and we end up with 000. So with twos-complements there are always 2 numbers that when negated will equal themself: 0 and the min.

]]> By: Adrian Sutton http://www.symphonious.net/2006/09/14/quick-java-puzzler/comment-page-1/#comment-32103 Adrian Sutton Thu, 14 Sep 2006 01:17:25 +0000 http://www.symphonious.net/2006/09/14/quick-java-puzzler/#comment-32103 Yep, in twos-compliment notation, you can always go one value more negative than you can positive (ie: if you can get to +3, you can get to -4). Yep, in twos-compliment notation, you can always go one value more negative than you can positive (ie: if you can get to +3, you can get to -4).

]]> By: Milo http://www.symphonious.net/2006/09/14/quick-java-puzzler/comment-page-1/#comment-32100 Milo Thu, 14 Sep 2006 00:51:45 +0000 http://www.symphonious.net/2006/09/14/quick-java-puzzler/#comment-32100 Oh, and its not like I figured that one out on my own, was one of the many interesting cases listed in a book I think I've mentioned before: Java™ Puzzlers: Traps, Pitfalls, and Corner Cases, by Joshua Bloch, Neal Gafter. If you find this puzzle interesting I highly recommend the book. It's up on safari - http://search.safaribooksonline.com - you can get a trial account for 2 weeks I think so won't even cost you anything. Oh, and its not like I figured that one out on my own, was one of the many interesting cases listed in a book I think I’ve mentioned before: Java™ Puzzlers: Traps, Pitfalls, and Corner Cases, by Joshua Bloch, Neal Gafter. If you find this puzzle interesting I highly recommend the book. It’s up on safari - http://search.safaribooksonline.com - you can get a trial account for 2 weeks I think so won’t even cost you anything.

]]> By: Milo http://www.symphonious.net/2006/09/14/quick-java-puzzler/comment-page-1/#comment-32097 Milo Thu, 14 Sep 2006 00:46:46 +0000 http://www.symphonious.net/2006/09/14/quick-java-puzzler/#comment-32097 That would be Integer.MIN_VALUE :) That would be Integer.MIN_VALUE :)

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