Add Java answer.

Author: junk0612

Diff for: Doukaku/E04/Main.class

@@ -1,5 +1,70 @@
+import java.util.Set;
+import java.util.HashSet;
+
 public class Main {
   public String solve(String input) {
-    return "";
+    StringBuilder builder = new StringBuilder();
+    Set<Integer> stonePath = getStonePath(input);
+    for (int i = 0; i < 8; i++) {
+      Set<Integer> manPath = getManPath(input, (char)(i + 'A'));
+      if (!manPath.removeAll(stonePath)) {
+        builder.append((char)('A' + i));
+      }
+    }
+    if (stonePath.isEmpty()) {
+      builder.deleteCharAt(builder.indexOf(input.substring(input.length() - 1)));
+    }
+    return builder.toString();
+  }
+
+  private Set<Integer> getManPath(String input, char position) {
+    String[] inputs = input.split(":");
+    String paths = inputs[0];
+    Set<Integer> manPath = new HashSet<>();
+    for (int i = paths.length() - 1; i >= 0; i--) {
+      char path = paths.charAt(i);
+      if (isClockwise(path, position)) {
+        manPath.add(i);
+        position = moveClockwise(position);
+      } else if (isCounterclockwise(path, position)) {
+        manPath.add(i);
+        position = moveCounterclockwise(position);
+      }
+    }
+    return manPath;
+  }
+
+  private Set<Integer> getStonePath(String input) {
+    String[] inputs = input.split(":");
+    String paths = inputs[0];
+    Set<Integer> stonePath = new HashSet<>();
+    char position = inputs[1].charAt(0);
+    for (int i = 0; i < paths.length(); i++) {
+      char path = paths.charAt(i);
+      if (isClockwise(path, position)) {
+        stonePath.add(i);
+        position = moveClockwise(position);
+      } else if (isCounterclockwise(path, position)) {
+        stonePath.add(i);
+        position = moveCounterclockwise(position);
+      }
+    }
+    return stonePath;
+  }
+
+  private boolean isClockwise(char path, char position) {
+    return (path - '0') % 8 == (position - 'A') % 8;
+  }
+
+  private boolean isCounterclockwise(char path, char position) {
+    return path - '1' == position - 'A';
+  }
+
+  private char moveClockwise(char position) {
+    return --position < 'A' ? 'H' : position;
+  }
+
+  private char moveCounterclockwise(char position) {
+    return ++position > 'H' ? 'A' : position;
   }
 }