refactor: revise obsolete solution logic (#852)

Return zero-size array with directions for empty input path.

Author: ParanoidUser

kata/6-kyu/shorter-path/main/ShortestPath.java

@@ -8,9 +8,9 @@ static String[] directions(String[] goal) {
     var stats = of(goal).collect(groupingBy(identity(), counting()));
     int y = (int) (stats.getOrDefault("N", 0L) - stats.getOrDefault("S", 0L));
     int x = (int) (stats.getOrDefault("E", 0L) - stats.getOrDefault("W", 0L));
-    return (
+    return x != 0 || y != 0  ? (
         "N".repeat(Math.max(0, y)) + "S".repeat(Math.max(0, -y)) +
         "E".repeat(Math.max(0, x)) + "W".repeat(Math.max(0, -x))
-    ).split("");
+    ).split("") : new String[0];
   }
 }

kata/6-kyu/shorter-path/test/DirectionsTest.java

@@ -7,10 +7,15 @@ class DirectionsTest {
   @ParameterizedTest
   @CsvSource(textBlock = """
       NNNNNENN, NNNNNNNE
+      SSNEWNWSE, S
       SSNEWSN, S
       NWSE,''
+      N, N
+      '', ''
       """)
   void sample(String path, String shortest) {
-    assertArrayEquals(shortest.split(""), ShortestPath.directions(path.split("")));
+    String[] goal = path.isEmpty() ? new String[0] : path.split("");
+    String[] expected = shortest.isEmpty() ? new String[0] : shortest.split("");
+    assertArrayEquals(expected, ShortestPath.directions(goal));
   }
 }