Computer Science Canada 2008 junior CCC question #4 |
| Author: | Horus [ Sat Dec 20, 2008 8:55 pm ] |
| Post subject: | 2008 junior CCC question #4 |
so i was just looking at last year's question here: http://cemc.math.uwaterloo.ca/contests/computing/2008/stage1/juniorEn.pdf and i couldn't figure out what question #4 means. i pretty much get polish notation but i don't understand how postfix notation works... and btw does --3+219 means (-3)-(2+1+9) ? just making sure... |
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| Author: | jbking [ Sat Dec 20, 2008 10:06 pm ] |
| Post subject: | RE:2008 junior CCC question #4 |
Not quite.... Remember that - a b means a - b and - + a b c means a+b - c as the + a b is evaluated first and then that answer is used an input for the next operator. - - 3 + 2 1 9 which equals :- - 3 (2+1) 9 which equals: - (3 - (2+1)) 9 which equals: 3 - (2+1) - 9 in infix notation which is different than you wrote. |
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| Author: | Horus [ Sat Dec 20, 2008 10:16 pm ] |
| Post subject: | RE:2008 junior CCC question #4 |
oh ok, kinda get it now but what about postfix notation? |
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| Author: | OneOffDriveByPoster [ Sat Dec 20, 2008 10:49 pm ] |
| Post subject: | Re: RE:2008 junior CCC question #4 |
Horus @ Sat Dec 20, 2008 10:16 pm wrote: oh ok, kinda get it now
Postfix is like how old calculators work:
but what about postfix notation? 3 2 - means you are calculating (3 - 2); the calculation happens as soon as the operator (-) is used. 3 2 - 1 + would be (3 - 2) + 1. 3 2 - 1 9 * + would be (3 - 2) + (1 * 9). |
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| Author: | Horus [ Sat Dec 20, 2008 10:54 pm ] |
| Post subject: | RE:2008 junior CCC question #4 |
ok thx i finally understand it now. now i can finally code haha. lol if this type of question appears on CCC in 2009 i'm probably screwed... |
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| Author: | Euphoracle [ Sun Dec 21, 2008 12:31 am ] |
| Post subject: | RE:2008 junior CCC question #4 |
When I did this, I was silly, and I converted it to our "regular" notation (in a sense), and then to the target format. I found it easier to work with a format I was comfortable with, and, although it wasn't the most efficient way of doing it, it got the job done correctly. I probably should have kept those solutions. Oh well. |
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