Add a sign-up snippet

.github/CODEOWNERS

@@ -1,6 +1,9 @@
 # Code owners
 .github/CODEOWNERS      @exercism/maintainers-admin
 
+# The code sample shown in the code check when people sign up to Exercism
+docs/SIGN_UP_SNIPPET.txt    @exercism/maintainers-admin
+
 # Changes to `fetch-configlet` should be made in the `exercism/configlet` repo
 bin/fetch-configlet     @exercism/maintainers-admin
 

docs/SIGN_UP_SNIPPET.txt

@@ -0,0 +1,12 @@
+public static String mostCommonWord(String text) {
+    Map<String, Integer> counts = new HashMap<>();
+    String best = "";
+    for (String word : text.toLowerCase().split(" ")) {
+        int count = counts.getOrDefault(word, 0) + 1;
+        counts.put(word, count);
+        if (count > counts.getOrDefault(best, 0)) {
+            best = word;
+        }
+    }
+    return String.format("\"%s\" appears %d times", best, counts.get(best));
+}