Add: leetcode/013.RomanToInteger

pixcai · Jan 3, 2018 · 9be3d83 · 9be3d83
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diff --git a/README.md b/README.md
@@ -10,3 +10,4 @@ Algorithms notes and code and leetcode solution by JavaScript
 - [008.StringToInteger](leetcode/008.StringToInteger)
 - [009.PalindromeNumber](leetcode/009.PalindromeNumber)
 - [010.RegularExpressionMatching](leetcode/010.RegularExpressionMatching)
+- [013.RomanToInteger](leetcode/013.RomanToInteger)
diff --git a/leetcode/013.RomanToInteger/013.RomanToInteger.js b/leetcode/013.RomanToInteger/013.RomanToInteger.js
@@ -0,0 +1,22 @@
+function romanToInt(s) {
+  const roman = {
+    I: 1,
+    V: 5,
+    X: 10,
+    L: 50,
+    C: 100,
+    D: 500,
+    M: 1000
+  }
+  const N = s.length - 1
+  let result = roman[s[N]]
+
+  for (let i = 0, c, n; i < N; i++) {
+    c = roman[s[i]]
+    n = roman[s[i + 1]]
+    result += c < n ? -c : c
+  }
+
+  return result
+}
+
diff --git a/leetcode/013.RomanToInteger/README.md b/leetcode/013.RomanToInteger/README.md
@@ -0,0 +1,13 @@
+### 代码实现
+[013.RomanToInteger](013.RomanToInteger.js)
+
+### 解题思路
+罗马数字有一个特征：两个相邻的字符，如果左边比右边大，那么两个数应该相加，如果左边比右边小，那么这两个数应该相减。根据这个特点，可以写出下面的计算过程：
+```js
+for (let i = 0, c, n; i < N; i++) {
+  c = roman[s[i]]
+  n = roman[s[i + 1]]
+  result += c < n ? -c : c
+}
+```
+依次将结果加上或减去罗马数的值，就将整个罗马数转换为了数字。