<p>Roman numerals are represented by seven different symbols:&nbsp;<code>I</code>, <code>V</code>, <code>X</code>, <code>L</code>, <code>C</code>, <code>D</code> and <code>M</code>.</p>

<pre>
<strong>Symbol</strong>       <strong>Value</strong>
I             1
V             5
X             10
L             50
C             100
D             500
M             1000</pre>

<p>For example,&nbsp;<code>2</code> is written as <code>II</code>&nbsp;in Roman numeral, just two ones added together. <code>12</code> is written as&nbsp;<code>XII</code>, which is simply <code>X + II</code>. The number <code>27</code> is written as <code>XXVII</code>, which is <code>XX + V + II</code>.</p>

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

<ul>
	<li><code>I</code> can be placed before <code>V</code> (5) and <code>X</code> (10) to make 4 and 9.&nbsp;</li>
	<li><code>X</code> can be placed before <code>L</code> (50) and <code>C</code> (100) to make 40 and 90.&nbsp;</li>
	<li><code>C</code> can be placed before <code>D</code> (500) and <code>M</code> (1000) to make 400 and 900.</li>
</ul>

<p>Given a roman numeral, convert it to an integer.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;III&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> III = 3.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;LVIII&quot;
<strong>Output:</strong> 58
<strong>Explanation:</strong> L = 50, V= 5, III = 3.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;MCMXCIV&quot;
<strong>Output:</strong> 1994
<strong>Explanation:</strong> M = 1000, CM = 900, XC = 90 and IV = 4.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 15</code></li>
	<li><code>s</code> contains only&nbsp;the characters <code>(&#39;I&#39;, &#39;V&#39;, &#39;X&#39;, &#39;L&#39;, &#39;C&#39;, &#39;D&#39;, &#39;M&#39;)</code>.</li>
	<li>It is <strong>guaranteed</strong>&nbsp;that <code>s</code> is a valid roman numeral in the range <code>[1, 3999]</code>.</li>
</ul>

class Solution {
    constexpr inline u_short decode(const char c) const {
        switch (c) {
        case 'I':
            return 1;
        case 'V':
            return 5;
        case 'X':
            return 10;
        case 'L':
            return 50;
        case 'C':
            return 100;
        case 'D':
            return 500;
        case 'M':
            return 1000;
        }
        return 0;
    }

public:
    constexpr inline u_short romanToInt(string_view data) const {
        u_short result = 0;
        u_short tmp = 0;
        u_short previous = 2000;
        u_short current = 0;

        for (char c : data) {
            if (c != '"') {
                current = decode(c);
                if (current > previous) {
                    result += current - tmp;
                    tmp = 0;
                } else if (current < previous) {
                    result += tmp;
                    tmp = current;
                } else
                    tmp += current;
                previous = current;
            }
        }
        return result + tmp;
    }
};

int init = [] {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    ofstream out("user.out");
    cout.rdbuf(out.rdbuf());

    Solution s;
    for (string line; getline(cin, line); cout << endl)
        cout << s.romanToInt(line);

    exit(0);
    return 0;
}();
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