LeetCode 12 - Integer to Roman - Python

 

Question:


Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.


Symbol Value
I 1
V 5
X 10
L 50
C 100
D 500
M 1000

For example, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

  • I can be placed before V (5) and X (10) to make 4 and 9. 
  • X can be placed before L (50) and C (100) to make 40 and 90. 
  • C can be placed before D (500) and M (1000) to make 400 and 900.

Given an integer, convert it to a roman numeral.

Example 1:
Input: num = 3
Output: "III"
Explanation: 3 is represented as 3 ones.

Example 2:
Input: num = 58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.

Example 3:
Input: num = 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.


Answer:


This code takes a non-negative integer as input and converts it into its corresponding Roman numeral representation. The approach used here is to store the Roman numeral values and their corresponding symbols in a vector of pairs. The algorithm then iterates through the vector and repeatedly adds the corresponding symbols to the result string while subtracting the corresponding value from the input integer until the input integer becomes zero.


Approach for this Problem:


  1. Initialize an empty string called Roman to store the resulting Roman numeral.
  2. Create a vector of pairs called storeIntRoman, to store the Roman numeral values and their corresponding symbols.
  3. Iterate through the storeIntRoman vector using a for loop.
  4. For each pair, check if the input integer is greater than or equal to the Roman numeral value.
  5. If it is, add the corresponding symbol to the Roman string and subtract the corresponding value from the input integer.
  6. Repeat steps 4-5 until the input integer becomes zero.
  7. Return the Roman string.

Code:

class Solution:
    def intToRoman(self, num: int) -> str:
        Roman = ""
        storeIntRoman = [[1000, "M"], [900, "CM"], [500, "D"], [400, "CD"], [100, "C"], [90, "XC"], [50, "L"], [40, "XL"], [10, "X"], [9, "IX"], [5, "V"], [4, "IV"], [1, "I"]]
        for i in range(len(storeIntRoman)):
            while num >= storeIntRoman[i][0]:
                Roman += storeIntRoman[i][1]
                num -= storeIntRoman[i][0]
        return Roman