feat: 刷题roman-to-integer

13.roman-to-integer.java

@@ -0,0 +1,82 @@
+/*
+ * @lc app=leetcode id=13 lang=java
+ *
+ * [13] Roman to Integer
+ */
+
+// @lc code=start
+
+import java.util.Arrays;
+
+class Solution {
+    public int romanToInt(String s) {
+        return romanToInt(0, s, 0);
+    }
+
+    private int romanToInt(int c, String s, int i) {
+        if(i == s.length()) {
+            return c;
+        }
+        int r;
+        if(i+1 < s.length() && COMBINED_FORMAT_LIST.contains(s.substring(i, i+2))) {
+            r = romanToInt(c+getValue(s.substring(i, i+2)), s, i+2);
+        } else {
+            r = romanToInt(c+getValue(s.substring(i, i+1)), s, i+1);
+        }
+        return r;
+    }
+
+    private int getValue(String s) {
+        int r = 0;
+        switch(s) {
+            case "IV":
+                r = 4;
+                break;
+            case "IX":
+                r = 9;
+                break;
+            case "XL":
+                r = 40;
+                break;
+            case "XC":
+                r = 90;
+                break;
+            case "CD":
+                r = 400;
+                break;
+            case "CM":
+                r = 900;
+                break;
+            case "I":
+                r = 1;
+                break;
+            case "V":
+                r = 5;
+                break;
+            case "X":
+                r = 10;
+                break;
+            case "L":
+                r = 50;
+                break;
+            case "C":
+                r = 100;
+                break;
+            case "D":
+                r = 500;
+                break;
+            case "M":
+                r = 1000;
+                break;
+            default: 
+                throw new RuntimeException("invalid expr: "+s);
+        }
+        return r;
+    }
+
+    public static final List<String> COMBINED_FORMAT_LIST = Arrays.asList(
+        "IV","IX", "XL", "XC", "CD", "CM"
+    );
+}
+// @lc code=end
+