add 0013 solution

Author: luojing

src/com/blankj/easy/_0009/LJSolution.java

@@ -1,5 +1,4 @@
 package com.blankj.easy._009;
-
 /**
  * @author luojing
  * @description LJSolution

src/com/blankj/easy/_0013/LJSolution.java

@@ -0,0 +1,40 @@
+package com.blankj.easy._013;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * @author luojing
+ * @description LJSolution
+ * @date 2022/07/17
+ */
+
+public class LJSolution {
+    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) {
+        LJSolution ljSolution = new LJSolution();
+        System.out.println(ljSolution.romanToInt("DCXXI")); // 621
+        System.out.println(ljSolution.romanToInt("CCCXLVIII")); // 348
+    }
+
+}