Reversing words is trickier than chars

Post #183,623 by Arkadiy 11/8/04 8:34:57 PM Reply	Reversing words is trickier than chars I don't think many people ever wrote this, except as an exersice. I would locate first and last word, picked the shorter of them, swapped the chars up to the shorter's size in place, and then I'd have to shift the whole buffer (mmemove) by 1 char to free the space for the next char of the long one to be copied. Of course, a better way is to have a fixed-size buffer (say, 8 chars) so that at least some words can be copied with a single shift. This produces slow and ugly code. In reality, I'd be sorely tempted to allocate another buffer and finish the whole thing with a single memcpy. Or am I missing an obvious and good algorithm here? -- This guy's ahead of his time! He's using quantum programming methods: in universes where invalid data is passed to this function, it does not return. Thus you are ensured that you will only have valid data after calling it. Optimally you'd destroy the universe on failure, but computers haven't quite advanced to that level yet. -- [link\|http://thedailywtf.com/archive/2004/10/26/2920.aspx\|The] Daily WTF
Post #183,632 by daemon 11/8/04 9:00:47 PM Reply	read the post above yours :-) read STDIN and assign variables to each non whitespace block, print them in reverse order. regards, daemon that way too many Iraqis conceived of free society as little more than a mosh pit with grenades. ANDISHEH NOURAEE
Post #183,644 by tuberculosis 11/8/04 9:26:37 PM Reply	You're missing an obvious and good solution Simply reverse the entire array by putting a pointer at each end and swapping chars until they pass each other. Now scan it for word breaks and reverse each word in place. Two passes, in place, no messy math. "The significant problems we face cannot be solved at the same level of thinking we were at when we created them." --Albert Einstein "This is still a dangerous world. It's a world of madmen and uncertainty and potential mental losses." --George W. Bush
Post #183,645 by Arkadiy 11/8/04 9:31:04 PM Reply	ohhh I guess I fail... -- This guy's ahead of his time! He's using quantum programming methods: in universes where invalid data is passed to this function, it does not return. Thus you are ensured that you will only have valid data after calling it. Optimally you'd destroy the universe on failure, but computers haven't quite advanced to that level yet. -- [link\|http://thedailywtf.com/archive/2004/10/26/2920.aspx\|The] Daily WTF
Post #183,650 by ben_tilly 11/8/04 10:31:24 PM Reply	An obvious but NOT necessarily good solution Consider the sentence, This sentence, right here, doesn't work well with Todd's algorithm. With Todd's algorithm we get the following, .algorithm s'Todd with well work t'doesn ,here right ,sentence This The output that I would expect (Arkadiy's algorithm would give it to you) is something more like, algorithm s, Todd with, well'work t doesn here right'sentence This. The best possible output would be, algorithm Todd's, with well, work doesn't here right sentence This. I hope that questioning the spec would give brownie points. Cheers, Ben I have come to believe that idealism without discipline is a quick road to disaster, while discipline without idealism is pointless. -- Aaron Ward (my brother)
Post #183,667 by tuberculosis 11/8/04 11:36:56 PM Reply	It gives the results I expect but your application of it I find odd. This sentence, right here, doesn't work well with Todd's algorithm. .algorithm s'Todd with well work t'doesn ,here right ,sentence This I don't think an appostrophe counts as a word boundary - either in a contraction or when using a possessive. So I don't understand how reversing Todd's gets you s'Todd or doesn't gets you t'doesn. As for the placement of punctuation - its kind of a fuzzy area I suppose and nobody is wrong as the desired behavior is left unspecified. The test string I had in mind was simpler - along the lines of "I was a bad boy". You can argue either result is correct. My gut is to treat sentence separators (commas, periods, etc) as individual words. You seem to have a different idea about leaving them between words 3 and 4 even if the original words 3 and 4 are now 9 and 8. I hope that questioning the spec would give brownie points. Pretty much any evidence of coherent thought gives brownie points. Failing completely but providing a view onto decent thought processes can still carry the day around here. We're just trying to find critical thinkers with decent grounding in CS that don't view all that "theoretical stuff" as useless. This is apparently pretty hard to find. "The significant problems we face cannot be solved at the same level of thinking we were at when we created them." --Albert Einstein "This is still a dangerous world. It's a world of madmen and uncertainty and potential mental losses." --George W. Bush
Post #183,753 by ben_tilly 11/9/04 11:24:29 AM Reply	I was assuming... the most naive definition of "word" - a string of word characters. In my experience people tend to start with that and then go from there. You're right that the spec did not specify what to do with the non-word characters. But when I hear, "Do this", my first question is, "What other side-effects are OK?" My default assumption tends to be "none" unless I find out otherwise. Cheers, Ben I have come to believe that idealism without discipline is a quick road to disaster, while discipline without idealism is pointless. -- Aaron Ward (my brother)

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