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Java-based LeetCode algorithm problem solutions, regularly updated
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package g0001_0100.s0012_integer_to_roman;

// #Medium #String #Hash_Table #Math #2023_08_09_Time_2_ms_(100.00%)_Space_43.2_MB_(81.21%)

/**
 * 12 - Integer to Roman\.
 *
 * Medium
 *
 * 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" 
 *
 * **Example 2:**
 *
 * **Input:** num = 4
 *
 * **Output:** "IV" 
 *
 * **Example 3:**
 *
 * **Input:** num = 9
 *
 * **Output:** "IX" 
 *
 * **Example 4:**
 *
 * **Input:** num = 58
 *
 * **Output:** "LVIII"
 *
 * **Explanation:** L = 50, V = 5, III = 3. 
 *
 * **Example 5:**
 *
 * **Input:** num = 1994
 *
 * **Output:** "MCMXCIV"
 *
 * **Explanation:** M = 1000, CM = 900, XC = 90 and IV = 4. 
 *
 * **Constraints:**
 *
 * *   `1 <= num <= 3999`
**/
public class Solution {
    public String intToRoman(int num) {
        StringBuilder sb = new StringBuilder();
        int m = 1000;
        int c = 100;
        int x = 10;
        int i = 1;
        num = numerals(sb, num, m, ' ', ' ', 'M');
        num = numerals(sb, num, c, 'M', 'D', 'C');
        num = numerals(sb, num, x, 'C', 'L', 'X');
        numerals(sb, num, i, 'X', 'V', 'I');
        return sb.toString();
    }

    private int numerals(StringBuilder sb, int num, int one, char cTen, char cFive, char cOne) {
        int div = num / one;
        switch (div) {
            case 9:
                sb.append(cOne);
                sb.append(cTen);
                break;
            case 8:
                sb.append(cFive);
                sb.append(cOne);
                sb.append(cOne);
                sb.append(cOne);
                break;
            case 7:
                sb.append(cFive);
                sb.append(cOne);
                sb.append(cOne);
                break;
            case 6:
                sb.append(cFive);
                sb.append(cOne);
                break;
            case 5:
                sb.append(cFive);
                break;
            case 4:
                sb.append(cOne);
                sb.append(cFive);
                break;
            case 3:
                sb.append(cOne);
                sb.append(cOne);
                sb.append(cOne);
                break;
            case 2:
                sb.append(cOne);
                sb.append(cOne);
                break;
            case 1:
                sb.append(cOne);
                break;
            default:
                break;
        }
        return num - (div * one);
    }
}