Leetcode 12 - Int to roman

Note:

  • First, we need to list all atomic roman numbers, including variant like 900, 90, 40....
  • For example, we list 90 instead of 80 is that 90 can be expressed as XC, but 80 is not XXC but LXXX.
  • While num is not 0, minus it with the biggest atmoic roman num available.
  • Keep doing this till num is 0.

Question:

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

1
2
3
4
5
6
7
8
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
2
Input: num = 3
Output: "III"

Code:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
/**
* @param {number} num
* @return {string}
*/
var intToRoman = function(num) {
const pairs = [[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']];
let res = '';
while (num !== 0) {
for (const [key, val] of pairs) {
while (num >= key) {
res += val;
num -= key;
}
}
}
return res;
};