[day8] there is a lie but i have been spoiled

src/main/java/CieDuVaseDesNoces/Day8.java

 package CieDuVaseDesNoces;
 
+import org.apache.commons.math3.util.ArithmeticUtils;
+
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
@@ -8,7 +10,6 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
-import java.util.stream.Stream;
 
 import static java.lang.Thread.currentThread;
 
@@ -26,8 +27,9 @@ class Day8 extends Day {
             reader.lines().forEach(line -> {
                 Matcher nodeMatcher = nodePattern.matcher(line);
                 if (!nodeMatcher.matches()) return;
-                network.put(nodeMatcher.group("from"), new ElementMap(
-                        nodeMatcher.group("left"), nodeMatcher.group("right")));
+                network.put(nodeMatcher.group("from"),
+                        new ElementMap(nodeMatcher.group("left"),
+                                nodeMatcher.group("right")));
             });
         } catch (IOException e) {
             throw new RuntimeException(e);
@@ -35,21 +37,32 @@ class Day8 extends Day {
     }
 
     String part1() {
-        return part1("AAA", "ZZZ");
+        return part1("AAA", "Z$");
     }
 
-    String part1(String startLabel, String targetLabel) {
+    String part1(String startLabel, String targetRegex) {
         String label = startLabel;
+        Pattern targetPattern = Pattern.compile(targetRegex);
         int step = 0;
         int length = instructions.length;
-        while (!label.equals(targetLabel)) {
-            label =  network.get(label).get(instructions[step++ % length]);
-        }
+        do {
+            label = network.get(label).get(instructions[step++ % length]);
+        } while (!targetPattern.matcher(label).find());
         return String.valueOf(step);
     }
 
     String part2() {
-        return null;
+        return part2("A$", "Z$");
+    }
+
+    String part2(String startRegex, String targetRegex) {
+        Pattern targetPattern = Pattern.compile(startRegex);
+        long ans = network.keySet().stream()
+                .filter(label -> targetPattern.matcher(label).find())
+                .map(label -> part1(label, targetRegex))
+                .mapToLong(Long::parseUnsignedLong)
+                .reduce(1, ArithmeticUtils::lcm);
+        return String.valueOf(ans);
     }
 
     static final class ElementMap extends HashMap<Character, String> {