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# Discussion on: LeetCode "13. Roman to Integer"

## Replies for: Besides pos += 1 appearing multiple times in the code, I think there is a bigger problem with s[pos] == symbols[numOfDigits][X]: it makes it diffic...

Takahiro Kudo

Wow! Thank you for the detailed explanation and code example!😍

I implemented:

``````ROMAN_TO_DECIMAL = {'I': 1, 'V':5, 'X':10, 'L':50, 'C':100, 'D': 500, 'M':1000}

len_s = len(s)
number = 0
for i in range(len_s - 1):
value = ROMAN_TO_DECIMAL[s[i]]
if ROMAN_TO_DECIMAL[s[i]] < ROMAN_TO_DECIMAL[s[i + 1]]:
number -= value
else:
number += value

# last
number += ROMAN_TO_DECIMAL[s[len_s - 1]]
return number
``````

I could not come up with the idea of `ROMAN_TO_DECIMAL`.😭

When thinking about this problem, did you first think about `ROMAN_TO_DECIMAL` and then the logic?
Or is the logic first?

If it's ok with you, could you tell me about your thought process?

I am sorry to disappoint you but I don't really know how I came up with this or in what order. I have solved this question a while ago.

`ROMAN_TO_DECIMAL` makes sense because for each roman numeral there is one corresponding number. There is a one to one mapping between them, and `dict` is python's map.

I think that the bottom line is experience. The more questions you solve on leetcode, see how other people's solutions look like, you develop more intuition as to what are the data-structures and algorithms suitable for each problem.

Also, you might find these books helpful, depends on what your goals are, and how much spare time you have:

1. Cracking the Coding Interview
2. Elements of Programming Interviews in Python