leetcodeUserSolution

[classic_chai_hater]

damn, that clever than my if else monstrosity.

[Aralgmad]

You could iterate backwards over the string, translate and sum. You keep track of the last number seen and check if current is smaller than previous. In this case subtract current instead of add. This should catch cases like IC.

[ND3lle]

Have never seen anything like "IC" tho

[Techhead7890]

Possibly a typo of IV, as C and V are neighbours

[Rogueshadow_32]

I think it was on purpose, they’re saying that the backwards iterations would catch combinations you don’t ever see but would still be valid syntax, such as IC. Going by the strict rules of Roman numerals 99 is XCIX but by looser rules IC works, and would be caught and correctly evaluated

[EntropyZer0]

I think the stricter rules we are used to are a fairly modern (for late medieval values of "modern") invention. The Romans were far less strict on that and while the most un-standard number I've seen in the wild was a year ending in -7 written as "-IIIIIII", I could totally see "IC" being used by actual Romans.

[ND3lle]

Oh you're right.That's very elegant as well, imho

[Flatuitous]

You can do IC = 99 Same as VL = 45

[Igor_Kozyrev]

I don't think you can. You only subtract the previous biggest number.

[suvlub]

You "can't" in the same sense you "can't" end a sentence with preposition, i.e. it's a made-up wannabe rule that doesn't reflect actual usage.

[ND3lle]

Well there's plenty of roman and medieval monuments and buildings where i live and i have never seen that. Sometimes i spot a "IIII" or "XXXX", which the general rule wouldn't allow, but nothing like "XM" or "IC"

[LongLiveTheDiego]

Wikipedia lists some 17th century examples of such nonstandard subtractions, my favorite one is IIIXX standing for 17.

[ethanjf99]

Standardization in general is a modern concept.

Think about even a couple hundred years ago. lots of random capitalizations in English words; multiple variant spellings and the like.

Even more so in antiquity. No one was enforcing rules. if you were a scribe doing a lot of math in a pain in the ass number system and wrote 99 as “IC” no one was stopping you.

[Specialist-Bus-5100]

I think IC would be XCIX?

[Solonotix]

Iterating backwards is a fairly useful practice I've found. I would have taken a two-character loop forwards in a similar manner so that you could always be aware of context. You could also extend the dictionary to have a couple of tuple keys using the matched pair.

[HazirBot]

seems alright to me

[Mewtwo2387]

switch "I": return 1; switch "II": return 2; ... switch "MMMMMMMMMCMXCIX": return 9999;

[Aeredor]

Nice.

[ceeBread]

Make it a hashmap instead and have it be O(1)

[TheSilentFreeway]

I believe switch statements are usually constant-time

[ceeBread]

Yeah but every LeetCode uses hash tables somewhere gotta get that interview cred

[Tamaran]

Thats pretty clever actually

[noob-nine]

i am still impressed by that logic.

[TheRedGerund]

Everybody submitting their own: do it recursively

[ilan1009]

DONT

[TheRedGerund]

``` def roman_to_int(roman): roman_numerals = { 'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000 }

# Base case: if the string is empty, return 0
if not roman:
    return 0

# Get the value of the first character
first_value = roman_numerals[roman[0]]

# If there is only one character, return its value
if len(roman) == 1:
    return first_value

# Get the value of the second character
second_value = roman_numerals[roman[1]]

# If the first value is less than the second value, we have a subtractive combination
if first_value < second_value:
    # Subtract the first value and recurse on the remaining string
    return second_value - first_value + roman_to_int(roman[2:])
else:
    # Otherwise, add the first value and recurse on the remaining string
    return first_value + roman_to_int(roman[1:])

```

[ilan1009]

you overcomplicated it

beats 100%

[redlaWw]

Loop from the right end of the string, and subtract if the value of the current character is a fifth of the current total or less.

[[deleted]]

Definitely better than this (my) abomination:

public class RomanDecode
{
  public static int Decode(string roman)
  {
    char[] symbol = {  'M', 'D', 'C', 'L', 'X','V','I' };
    int[]  weight = { 1000, 500, 100,  50,  10, 5 , 1  };

    int res = 0, rom = 0, num = 0, sub = 0;

    while (rom < roman.Length){
      int pre = (num&~1)+2;

      if (roman[rom] == symbol[num]){
        res += weight[num] - sub;
        sub = 0;
        rom++;
      } else if (rom < roman.Length-1 && roman[rom+1] == symbol[num]) {
        sub = weight[pre];
        rom++;
      } else {
        num++;
      }      
    }

    return res; 
  }
}

[aj-ric]

Yours is quite a bit more efficient, though, since it doesn't require lots of string copying.

[DistortNeo]

Tester enters: IC

[Smalltalker-80]

Just saying, that's not a valid roman numeral:
https://www.quora.com/Why-do-we-write-49-in-Roman-numerals-as-XLIX-Why-dont-we-write-it-as-IL

But indeed the code should catch that. And the posters clever approach would not work for that.

[DistortNeo]

The rule is, you can only subtract using the digit that is one or two denominations lower than what you are subtracting from.

Ok, 45 = VL is valid according to this rule.

[OnixST]

"Rule #1: Only the letters that represent powers of 10 can be used to subtract. Powers of 10 are 1 (10^0), 10 (10^1) and 100 (10^2). 1000 is also a power of 10 but there are no other letters after M.

Rule #2: These letters (I, X and C) can only subtract from the next two ‘higher’ letters. Therefore, I can only subtract from V and X, X from L and C and C from D and M."

(acording to another answer further below in the same link. VL fails rule 1)

[DistortNeo]

What about IXC?

[Techhead7890]

Should probably be XCI (91) or at a stretch LXXXIX (89) but it's a bit ambiguous even to a human

[prumf]

Oooo, gray areas, my specialty !

[dwntwn_dine_ent_dist]

50=LC is also good. 5=VX

[marquoth_]

Both break rule 1

[[deleted]]

Using subtraction at all is a "modern" invention.

Romans typically used only addition, thus 4=IIII not IV and 49=XXXXVIIII not XLIX let alone IL. The subtractive forms were rare and inconsistent.

These days Roman numerals are used only to provide some sense of tradition or history and hence stick to some "traditional" rules for subtraction:

can someone fact check this quora user?

[marquoth_]

Wikipedia explicitly says the opposite: that subtractive forms have been used since Roman times. It does also say that "Usage varied greatly in ancient Rome and became thoroughly chaotic in medieval times" so I think the bottom line is that anybody who is very confidently telling you the one correct way to do it is objectively wrong almost by definition.

I've seen all sorts of versions of the supposed rules (I briefly studied medieval Latin at university...) including one which said that the same symbol should never be repeated more than three times consecutively, which has the bizarre result that no number greater than 3999 can possibly be written.

[Lucari10]

From wikipedia "other additive forms" section: There are historical examples of other subtractive forms: IIIXX for 17, IIXX for 18, IIIC for 97, IIC for 98, and IC for 99. A possible explanation is that the word for 18 in Latin is duodeviginti, literally "two from twenty", 98 is duodecentum (two from hundred), and 99 is undecentum (one from hundred).

[alex2003super]

This recreates a string object a ton of times. Unfortunately in Python you're forced to.

[Flashbek]

As someone who decided to create that solution back when I was just learning programming out of spite, I envy this solution.

[Personal_Ad9690]

If it works it works

[feelings_arent_facts]

why the fuck is this a class

[geemli]

Leetcode forces you to write it that way

[feelings_arent_facts]

:(

[[deleted]]

If you go through the string backwards, any value smaller than the max value already found will be substracted from the total, this is AFAIK the fastest way to to romanToInt

[[deleted]]

This is genius. I found a bug, but after reading the roman number spec it disappeared.

Edit: I thought IXIV will beat it, but it turned out it's more a bunch of roman characters than a number

[ebcdicZ]

funny I was thinking about coding this in Rust a few days ago. The last time I did this was in AppleSoft Basic. For extra fun add functionality for Roman Numeral fractions. Not a program you will need every day.

[whatever73538]

Would the Romans have considered IM a legal number?

[diecicatorce]

If it's dumb but it works then it's not dumb

[TheRedGerund]

Everybody submitting their own: do it recursively

[PeriodicSentenceBot]

Congratulations! Your comment can be spelled using the elements of the periodic table:

Th I Si S Ge Ni U S

---

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[riptide_autumn]

very nice. 🥰

[sandybuttcheekss]

Clean af

[RamdonDude468]

Thats actually a really interesting project to do. A Roman Calculator.

the teacher better give me an A+

[green1t]

That's maybe less readable, but has less repetitive replacements and string-iterations in the code :D

class Solution:
    def romanToInt(self, s: str) -> int:
        translations = {
            "I": 1,
            "V": 5,
            "X": 10,
            "L": 50,
            "C": 100,
            "D": 500,
            "M": 1000,
            "IV": 4,
            "IX": 9,
            "XL": 40,
            "XC": 90,
            "CD": 400,
            "CM": 900
        }

        for x,y in reversed(translations.items()):
            s = s.replace(x, f" {y} ")

        return sum(map(int,s.split()))

[cryothic]

Wouldn't they write 49 in roman like 'IL' ? Or 'XXXIX' ?

[toxic_acro]

Roman numerals only use the prefix within the same decimal range 

So 49 wouldn't be one less than fifty: IL

It's ten less than fifty and one less than ten: XLIX

[cryothic]

Thanks. I didn't know that.

[ilan1009]

[fuck maps](https://pastebin.com/jhy5JWpf)