12. Integer to Roman

Medium
Hash Table Math String

Seven different symbols represent Roman numerals with the following values:

Symbol

Value

I

1

V

5

X

10

L

50

C

100

D

500

M

1000

Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules:

  • If the value does not start with 4 or 9, select the symbol of the maximal value that can be subtracted from the input, append that symbol to the result, subtract its value, and convert the remainder to a Roman numeral.
  • If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol, for example, 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD) and 900 (CM).
  • Only powers of 10 (I, X, C, M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V), 50 (L), or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form.

Given an integer, convert it to a Roman numeral.

Example 1:

Input: num = 3749

Output: “MMMDCCXLIX”

Explanation:

3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M)
 700 = DCC as 500 (D) + 100 (C) + 100 (C)
  40 = XL as 10 (X) less of 50 (L)
   9 = IX as 1 (I) less of 10 (X)
Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places

Example 2:

Input: num = 58

Output: “LVIII”

Explanation:

50 = L
 8 = VIII

Example 3:

Input: num = 1994

Output: “MCMXCIV”

Explanation:

1000 = M
 900 = CM
  90 = XC
   4 = IV

Constraints:

  • 1 <= num <= 3999
func intToRoman(num int) string {
	result := ""

	keys := []string{"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"}
	values := []int{1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1}

	for i := range keys {
		// fmt.Println("KV", keys[i], values[i])
		for num >= values[i] {
			result += keys[i]
			num -= values[i]
			// fmt.Println("Taking", values[i], result)
		}
	}

	return result
}