add 013

Author: Blankj

README.md

@@ -10,6 +10,7 @@
 |7|[Reverse Integer][007]|Math|
 |8|[String to Integer (atoi)][008]|Math, String|
 |9|[Palindrome Number][009]|Math|
+|13|[Roman to Integer][013]|Math, String|
 
 
 ## Medium
@@ -34,3 +35,4 @@
 [007]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/007/README.md
 [008]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/008/README.md
 [009]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/009/README.md
+[013]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/013/README.md

note/001/README.md

@@ -15,7 +15,7 @@ Because nums[0] + nums[1] = 2 + 7 = 9,
 return [0, 1].
 ```
 
-**Tags：** Array, Hash Table
+**Tags:** Array, Hash Table
 
 
 ## 思路0

note/007/README.md

@@ -8,7 +8,7 @@ Reverse digits of an integer.
 
 **Example2:** x = -123, return -321
 
-**Spoilers：**
+**Spoilers:**
 
 **Have you thought about this?**
 
@@ -24,7 +24,7 @@ For the purpose of this problem, assume that your function returns 0 when the re
 
 The input is assumed to be a 32-bit signed integer. Your function should **return 0 when the reversed integer overflows**.
 
-**Tags：** Math
+**Tags:** Math
 
 
 ## 思路

note/008/README.md

@@ -8,7 +8,7 @@ Implement atoi to convert a string to an integer.
 
 **Notes:** It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.
 
-**Spoilers：**
+**Spoilers:**
 
 **Requirements for atoi:**
 

note/009/README.md

@@ -4,7 +4,7 @@
 
 Determine whether an integer is a palindrome. Do this without extra space.
 
-**spoilers:**
+**Spoilers:**
 
 **Some hints:**
 
@@ -16,7 +16,7 @@ You could also try reversing an integer. However, if you have solved the problem
 
 There is a more generic way of solving this problem.
 
-**Tags：** Math
+**Tags:** Math
 
 
 ## 思路0

note/013/README.md

@@ -0,0 +1,45 @@
+# [Roman to Integer](https://leetcode.com/problems/roman-to-integer/)
+
+## Description
+
+Given a roman numeral, convert it to an integer.
+
+Input is guaranteed to be within the range from 1 to 3999.
+
+**Tags:** Math, String
+
+
+## 思路0
+
+题意是罗马数字转整型数，范围从1到3999，查看下百度百科的罗马数字介绍如下，
+
+* 相同的数字连写，所表示的数等于这些数字相加得到的数，如 Ⅲ=3；
+* 小的数字在大的数字的右边，所表示的数等于这些数字相加得到的数，如 Ⅷ=8、Ⅻ=12；
+* 小的数字（限于 Ⅰ、X 和 C）在大的数字的左边，所表示的数等于大数减小数得到的数，如 Ⅳ=4、Ⅸ=9；
+
+那么我们可以利用map来完成罗马数字的7个数字符号：I、V、X、L、C、D、M和整数的映射关系，然后根据上面的解释来模拟完成即可。
+
+``` java
+public class Solution {
+    public int romanToInt(String s) {
+        Map<Character, Integer> map = new HashMap<>();
+        map.put('I', 1);
+        map.put('V', 5);
+        map.put('X', 10);
+        map.put('L', 50);
+        map.put('C', 100);
+        map.put('D', 500);
+        map.put('M', 1000);
+        int len = s.length();
+        int sum = map.get(s.charAt(len - 1));
+        for (int i = len - 2; i >= 0; --i) {
+            if (map.get(s.charAt(i)) < map.get(s.charAt(i + 1))) {
+                sum -= map.get(s.charAt(i));
+            } else {
+                sum += map.get(s.charAt(i));
+            }
+        }
+        return sum;
+    }
+}
+```

project/LeetCode/leetcode/src/main/java/com/blankj/easy/_013/Solution.java

@@ -0,0 +1,41 @@
+package com.blankj.easy._013;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * <pre>
+ *     author: Blankj
+ *     blog  : http://blankj.com
+ *     time  : 2017/04/22
+ *     desc  :
+ * </pre>
+ */
+public class Solution {
+    public int romanToInt(String s) {
+        Map<Character, Integer> map = new HashMap<>();
+        map.put('I', 1);
+        map.put('V', 5);
+        map.put('X', 10);
+        map.put('L', 50);
+        map.put('C', 100);
+        map.put('D', 500);
+        map.put('M', 1000);
+        int len = s.length();
+        int sum = map.get(s.charAt(len - 1));
+        for (int i = len - 2; i >= 0; --i) {
+            if (map.get(s.charAt(i)) < map.get(s.charAt(i + 1))) {
+                sum -= map.get(s.charAt(i));
+            } else {
+                sum += map.get(s.charAt(i));
+            }
+        }
+        return sum;
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.romanToInt("DCXXI"));// 621
+        System.out.println(solution.romanToInt("CCCXLVIII"));// 384
+    }
+}