[Math] add Solution to Roman to Integer

Yi Gu · Yi Gu · commit ad01e5bdc364 · 2016-06-15T20:58:37.000-07:00
diff --git a/Math/RomanToInteger.swift b/Math/RomanToInteger.swift
@@ -0,0 +1,41 @@
+/**
+ * Question Link: https://leetcode.com/problems/roman-to-integer/
+ * Primary idea: Iterate through end to start, add or minus according to different situations
+ * Time Complexity: O(n), Space Complexity: O(n)
+ *
+ */
+
+class RomanToInteger {
+    func romanToInt(s: String) -> Int {
+        let dict = initDict()
+        let chars = [Character](s.characters.reverse())
+        var res = 0
+        
+        for i in 0 ..< chars.count {
+            guard let current = dict[String(chars[i])] else {
+                return res
+            }
+            if i > 0 && current < dict[String(chars[i - 1])] {
+                res -= current
+            } else {
+                res += current
+            }
+        }
+        
+        return res
+    }
+    
+    private func initDict() -> [String: Int] {
+        var dict = [String: Int]()
+        
+        dict["I"] = 1
+        dict["V"] = 5
+        dict["X"] = 10
+        dict["L"] = 50
+        dict["C"] = 100
+        dict["D"] = 500
+        dict["M"] = 1000
+        
+        return dict
+    }
+}
