roman-to-integer.md

<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;two is written as <code>II</code>&nbsp;in Roman numeral, just two one&#39;s added together. Twelve is written as, <code>XII</code>, which is simply <code>X</code> + <code>II</code>. The number twenty seven is written as <code>XXVII</code>, which is <code>XX</code> + <code>V</code> + <code>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. Input is guaranteed to be within the range from 1 to 3999.</p>

<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong>&nbsp;&quot;III&quot;
<strong>Output:</strong> 3</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong>&nbsp;&quot;IV&quot;
<strong>Output:</strong> 4</pre>

<p><strong>Example 3:</strong></p>

<pre>
<strong>Input:</strong>&nbsp;&quot;IX&quot;
<strong>Output:</strong> 9</pre>

<p><strong>Example 4:</strong></p>

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

<p><strong>Example 5:</strong></p>

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