Create roman-to-integer.cpp

Author: kamyu104

C++/roman-to-integer.cpp

@@ -0,0 +1,20 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    int romanToInt(string s) {
+        unordered_map<char, int> numeral_map = {{'I',    1}, {'V',   5}, {'X',  10},
+                                                {'L',   50}, {'C', 100}, {'D', 500},
+                                                {'M', 1000}};
+        int decimal = 0;
+        for (int i = 0; i < s.length(); ++i) {
+            if (i > 0 && numeral_map[s[i]] > numeral_map[s[i - 1]]) {
+                decimal += numeral_map[s[i]] - 2 * numeral_map[s[i - 1]];
+            } else {
+                decimal += numeral_map[s[i]];
+            }
+        }
+        return decimal;
+    }
+};