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package g0001_0100.s0013_roman_to_integer;

// #Easy #Top_Interview_Questions #String #Hash_Table #Math
// #2023_08_09_Time_2_ms_(100.00%)_Space_44.1_MB_(19.16%)

/**
 * 13 - Roman to Integer\.
 *
 * Easy
 *
 * 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 a roman numeral, convert it to an integer.
 *
 * **Example 1:**
 *
 * **Input:** s = "III"
 *
 * **Output:** 3 
 *
 * **Example 2:**
 *
 * **Input:** s = "IV"
 *
 * **Output:** 4 
 *
 * **Example 3:**
 *
 * **Input:** s = "IX"
 *
 * **Output:** 9 
 *
 * **Example 4:**
 *
 * **Input:** s = "LVIII"
 *
 * **Output:** 58
 *
 * **Explanation:** L = 50, V= 5, III = 3. 
 *
 * **Example 5:**
 *
 * **Input:** s = "MCMXCIV"
 *
 * **Output:** 1994
 *
 * **Explanation:** M = 1000, CM = 900, XC = 90 and IV = 4. 
 *
 * **Constraints:**
 *
 * *   `1 <= s.length <= 15`
 * *   `s` contains only the characters `('I', 'V', 'X', 'L', 'C', 'D', 'M')`.
 * *   It is **guaranteed** that `s` is a valid roman numeral in the range `[1, 3999]`.
**/
public class Solution {
    public int romanToInt(String s) {
        int x = 0;
        char y;
        for (int i = 0; i < s.length(); i++) {
            y = s.charAt(i);
            switch (y) {
                case 'I':
                    x = getX(s, x, i, 1, 'V', 'X');
                    break;
                case 'V':
                    x += 5;
                    break;
                case 'X':
                    x = getX(s, x, i, 10, 'L', 'C');
                    break;
                case 'L':
                    x += 50;
                    break;
                case 'C':
                    x = getX(s, x, i, 100, 'D', 'M');
                    break;
                case 'D':
                    x += 500;
                    break;
                case 'M':
                    x += 1000;
                    break;
                default:
                    break;
            }
        }
        return x;
    }

    private int getX(String s, int x, int i, int i2, char v, char x2) {
        if (i + 1 == s.length()) {
            x += i2;
        } else if (s.charAt(i + 1) == v) {
            x -= i2;
        } else if (s.charAt(i + 1) == x2) {
            x -= i2;
        } else {
            x += i2;
        }
        return x;
    }
}