Assignment on my birthday

script.js

@@ -1,12 +1,16 @@
 const ASSIGNMENT = 'assignment';
 const ANSWER = 'answer';
+const ALGORITHM_CHECKBOX = 'algorithm';
+const MARKER_DISTINCT_CHARACTERS = 4;
+const MESSAGE_DISTINCT_CHARACTERS = 14;
 const NEWLINE_CHARACTER = '\n';
 
 /**
  * Main function
  */
 window.onload = function() {
-    document.getElementById(ASSIGNMENT).addEventListener("input", calculateAnswer);
+  document.getElementById(ASSIGNMENT).addEventListener("input", calculateAnswer);
+  document.getElementById(ALGORITHM_CHECKBOX).addEventListener("click", calculateAnswer);
 }
 
 /**
@@ -15,7 +19,9 @@ window.onload = function() {
  */
 function calculateAnswer(event) {
   console.info("Calculating answer for input...");
-  let answer = algorithm(event.target.value);
+  let assignment = document.getElementById(ASSIGNMENT).value;
+  let distinctCharacters = (document.getElementById(ALGORITHM_CHECKBOX).checked)? MESSAGE_DISTINCT_CHARACTERS: MARKER_DISTINCT_CHARACTERS;
+  let answer = algorithm(assignment, distinctCharacters);
 
   document.getElementById(ANSWER).innerText = answer;
 }
@@ -25,9 +31,28 @@ function calculateAnswer(event) {
  * @param assignment the input from the assignment.
  * @return string the answer
  */
-function algorithm(assignment) {
-    let lines = assignment.trim().split(NEWLINE_CHARACTER);
-    console.info("Linecount:" + lines.length);
+function algorithm(assignment, distinctCharacters) {
+    let signal = assignment.trim();
+    let marker = assignment.substring(0,distinctCharacters);
 
-    // TODO: implement assignment
+    for(let i=distinctCharacters; i<signal.length; i++) {
+      if(containsDistinctCharacters(marker)) {
+        console.debug("Found marker after:" + i + " characters");
+        return "Marker found after processing: " + i + " characters.";
+      }
+
+      marker = marker.substring(1, distinctCharacters) + assignment[i];
+    }
+
+    return "No marker found.";
+}
+
+/**
+ * Check if string only contains distinct characters.
+ * @param String string the string to check
+ * @return true, if string contains only distinct characters
+ */
+function containsDistinctCharacters(string) {
+  console.debug("Check marker: " + string);
+  return new Set(string).size == string.length;
 }