Added task 13.

Author: javadev

Diff for: src/main/java/s0013.roman.to.integer/Solution.java

@@ -0,0 +1,59 @@
+package s0013.roman.to.integer;
+
+public class Solution {
+    public int romanToInt(String s) {
+        int x = 0;
+        char y;
+        for (int i = 0; i < s.length(); i++) {
+            y = s.charAt(i);
+            switch (y) {
+                case 'I':
+                    if (i + 1 == s.length()) {
+                        x += 1;
+                    } else if (s.charAt(i + 1) == 'V') {
+                        x -= 1;
+                    } else if (s.charAt(i + 1) == 'X') {
+                        x -= 1;
+                    } else {
+                        x += 1;
+                    }
+                    break;
+                case 'V':
+                    x += 5;
+                    break;
+                case 'X':
+                    if (i + 1 == s.length()) {
+                        x += 10;
+                    } else if (s.charAt(i + 1) == 'L') {
+                        x -= 10;
+                    } else if (s.charAt(i + 1) == 'C') {
+                        x -= 10;
+                    } else {
+                        x += 10;
+                    }
+                    break;
+                case 'L':
+                    x += 50;
+                    break;
+                case 'C':
+                    if (i + 1 == s.length()) {
+                        x += 100;
+                    } else if (s.charAt(i + 1) == 'D') {
+                        x -= 100;
+                    } else if (s.charAt(i + 1) == 'M') {
+                        x -= 100;
+                    } else {
+                        x += 100;
+                    }
+                    break;
+                case 'D':
+                    x += 500;
+                    break;
+                case 'M':
+                    x += 1000;
+                    break;
+            }
+        }
+        return x;
+    }
+}

Diff for: src/test/java/s0013.roman.to.integer/SolutionTest.java

@@ -0,0 +1,13 @@
+package s0013.roman.to.integer;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.Test;
+
+public class SolutionTest {
+    @Test
+    public void romanToInt() {
+        assertThat(new Solution().romanToInt("III"), equalTo(3));
+    }
+}