No13.java

Author: tujietg

README.md

@@ -55,6 +55,7 @@ I really **enjoy** it, I will always update it.
 | ------------------------------------------------------------ | ------------------------------------------------------------ | ---- | ---------- | ---- |
 | [7.Reverse Integer](https://leetcode.com/problems/reverse-integer) | [java](https://github.com/tujietg/leetcode/blob/master/math/No07.java) |      | Easy       |      |
 | [9.Palindrome Number](https://leetcode.com/problems/palindrome-number) | [java](https://github.com/tujietg/leetcode/blob/master/math/No09.java) | O(N) | Easy       |      |
+| [13.Roman to Integer](https://leetcode.com/problems/roman-to-integer) | [java](https://github.com/tujietg/leetcode/blob/master/math/No13.java) | O(N) | Easy       |      |
 
 
 

math/No13.java

@@ -0,0 +1,20 @@
+class Solution {
+    public int romanToInt(String s) {
+        int sum = 0;
+        if(s.indexOf("IV") != -1 || s.indexOf("IX") != -1){sum -= 2;}
+        if(s.indexOf("XL") != -1 || s.indexOf("XC") != -1){sum -= 20;}
+        if(s.indexOf("CD") != -1 || s.indexOf("CM") != -1){sum -= 200;}
+        char[] ch = s.toCharArray();
+        
+        for(int i = 0; i < ch.length; i++){
+            if(ch[i] == 'I'){sum += 1;}
+            if(ch[i] == 'V'){sum += 5;}
+            if(ch[i] == 'X'){sum += 10;}
+            if(ch[i] == 'L'){sum += 50;}
+            if(ch[i] == 'C'){sum += 100;}
+            if(ch[i] == 'D'){sum += 500;}
+            if(ch[i] == 'M'){sum += 1000;}
+        }
+        return sum;    
+    }
+}