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Description
tab: English
<p>Roman numerals are represented by seven different symbols: <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, <code>2</code> is written as <code>II</code> in Roman numeral, just two ones added together. <code>12</code> is written as <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. </li>
<li><code>X</code> can be placed before <code>L</code> (50) and <code>C</code> (100) to make 40 and 90. </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> </p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong> s = "III"
<strong>Output:</strong> 3
<strong>Explanation:</strong> III = 3.
</pre>
<p><strong class="example">Example 2:</strong></p>
<pre>
<strong>Input:</strong> s = "LVIII"
<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 = "MCMXCIV"
<strong>Output:</strong> 1994
<strong>Explanation:</strong> M = 1000, CM = 900, XC = 90 and IV = 4.
</pre>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>1 <= s.length <= 15</code></li>
<li><code>s</code> contains only the characters <code>('I', 'V', 'X', 'L', 'C', 'D', 'M')</code>.</li>
<li>It is <strong>guaranteed</strong> that <code>s</code> is a valid roman numeral in the range <code>[1, 3999]</code>.</li>
</ul>
> [!tip]- Hint 1
>
> Problem is simpler to solve by working the string from back to front and using a map.
---
[submissions](https://leetcode.com/problems/roman-to-integer/submissions/) | [solutions](https://leetcode.com/problems/roman-to-integer/solutions/)
tab: 中文
<p>罗马数字包含以下七种字符: <code>I</code>， <code>V</code>， <code>X</code>， <code>L</code>，<code>C</code>，<code>D</code> 和 <code>M</code>。</p>
<pre>
<strong>字符</strong> <strong>数值</strong>
I 1
V 5
X 10
L 50
C 100
D 500
M 1000</pre>
<p>例如， 罗马数字 <code>2</code> 写做 <code>II</code> ，即为两个并列的 1 。<code>12</code> 写做 <code>XII</code> ，即为 <code>X</code> + <code>II</code> 。 <code>27</code> 写做 <code>XXVII</code>, 即为 <code>XX</code> + <code>V</code> + <code>II</code> 。</p>
<p>通常情况下，罗马数字中小的数字在大的数字的右边。但也存在特例，例如 4 不写做 <code>IIII</code>，而是 <code>IV</code>。数字 1 在数字 5 的左边，所表示的数等于大数 5 减小数 1 得到的数值 4 。同样地，数字 9 表示为 <code>IX</code>。这个特殊的规则只适用于以下六种情况：</p>
<ul>
<li><code>I</code> 可以放在 <code>V</code> (5) 和 <code>X</code> (10) 的左边，来表示 4 和 9。</li>
<li><code>X</code> 可以放在 <code>L</code> (50) 和 <code>C</code> (100) 的左边，来表示 40 和 90。 </li>
<li><code>C</code> 可以放在 <code>D</code> (500) 和 <code>M</code> (1000) 的左边，来表示 400 和 900。</li>
</ul>
<p>给定一个罗马数字，将其转换成整数。</p>
<p> </p>
<p><strong>示例 1:</strong></p>
<pre>
<strong>输入:</strong> s = "III"
<strong>输出:</strong> 3</pre>
<p><strong>示例 2:</strong></p>
<pre>
<strong>输入:</strong> s = "IV"
<strong>输出:</strong> 4</pre>
<p><strong>示例 3:</strong></p>
<pre>
<strong>输入:</strong> s = "IX"
<strong>输出:</strong> 9</pre>
<p><strong>示例 4:</strong></p>
<pre>
<strong>输入:</strong> s = "LVIII"
<strong>输出:</strong> 58
<strong>解释:</strong> L = 50, V= 5, III = 3.
</pre>
<p><strong>示例 5:</strong></p>
<pre>
<strong>输入:</strong> s = "MCMXCIV"
<strong>输出:</strong> 1994
<strong>解释:</strong> M = 1000, CM = 900, XC = 90, IV = 4.</pre>
<p> </p>
<p><strong>提示：</strong></p>
<ul>
<li><code>1 <= s.length <= 15</code></li>
<li><code>s</code> 仅含字符 <code>('I', 'V', 'X', 'L', 'C', 'D', 'M')</code></li>
<li>题目数据保证 <code>s</code> 是一个有效的罗马数字，且表示整数在范围 <code>[1, 3999]</code> 内</li>
<li>题目所给测试用例皆符合罗马数字书写规则，不会出现跨位等情况。</li>
<li>IL 和 IM 这样的例子并不符合题目要求，49 应该写作 XLIX，999 应该写作 CMXCIX 。</li>
<li>关于罗马数字的详尽书写规则，可以参考 <a href="https://baike.baidu.com/item/%E7%BD%97%E9%A9%AC%E6%95%B0%E5%AD%97/772296">罗马数字 - 百度百科</a>。</li>
</ul>
> [!tip]- 提示 1
>
> Problem is simpler to solve by working the string from back to front and using a map.
---
[提交记录](https://leetcode.cn/problems/roman-to-integer/submissions/) | [题解](https://leetcode.cn/problems/roman-to-integer/solution/)
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