• rooroo@feddit.org
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    2 days ago

    It also works the other way round: wanna convert Arabic n to Roman? Just write n times ‘I’ and revert these replacement in inverse order.

    • lugal@lemmy.dbzer0.com
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      2 days ago

      I don’t know what happens when the substring overlaps. Like for the number 6, will it replace the first 5 I’s with V and end up correctly with VI or the last ones and come to IV? I would guess the former and maybe you know but I never thought about it before

      • rooroo@feddit.org
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        1 day ago

        I’ve written it that way and it works, as in it will replace left to right and you replace iiii to iv after iiiii to v

        • lugal@lemmy.dbzer0.com
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          1 day ago

          Makes sense but it will fail at 9 (VIV) it would only work for 9 if the replace went from right to left or the V and IV statements were exchanged but in both cases, 6 would fail

          • rooroo@feddit.org
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            13 hours ago

            9 is IX though, and that works.

            6 works fine, as it replaces the first set of 5 I with V and then there’s nothing to replace.

            I’d written it in typescript for all it’s worth; go ahead and try it yourself :)

              • rooroo@feddit.org
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                7 hours ago

                I like your questions about this and they all seem fair but I kinda wanna encourage you to go ahead and write it yourself; it’s a fun way to convert into Roman numerals that both is and isn’t intuitive at the same time.

              • rooroo@feddit.org
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                7 hours ago

                No, cause you do the replacement from large to small, I.e. you’d first check for 10 I to replace with X (none found); then replace 9 with IX (check), then check for 5, 4 and so on.

                • lugal@lemmy.dbzer0.com
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                  7 hours ago

                  The original doesn’t have an extra check for 9 and it works for Roman->Indioarabic because it’s:

                  IX
                  ->IVV
                  ->IIIIV
                  ->IIIIIIIII
                  

                  But the other way around, you need an extra step for 9. That’s where our misunderstanding comes from.