Move all solutions into separate directory (cleanup)

the beginning

solutions/roman-to-integer/Solution.java

@@ -0,0 +1,35 @@
+// Accepted
+// Runtime: 4ms
+// Memory Usage: 39.3 MB
+// Submitted: January 15th, 2021
+
+class Solution {
+    Map<Character, Integer> convert = new HashMap<Character, Integer>();
+    
+    public Solution() {
+        char[] symbols = new char[]{'I', 'V', 'X', 'L', 'C', 'D', 'M'};
+        int[] values = new int[]{1, 5, 10, 50, 100, 500, 1000};
+        
+        for (int i = 0; i < symbols.length; i++)
+            convert.put(symbols[i], values[i]);
+    }
+    
+    public int romanToInt(String s) {
+        int n = s.length();
+        int sum = 0;
+        int prev = convert.get(s.charAt(0));
+        int cur = 0;
+        
+        for (int i = 1; i < n; i++) {
+            cur = convert.get(s.charAt(i));
+            if (prev < cur)
+                cur -= prev;
+            else
+                sum += prev;
+            prev = cur;
+        }
+        sum += prev;
+        
+        return sum;
+    }
+}