solved 2

src/Problem2.java

@@ -13,44 +13,73 @@ public class Problem2 {
 
         try {
             String input = readFileAsString(filePath);
-            List<Long> numbers = parseRanges(input);
+            List<long[]> ranges = parseRanges(input);
-
+            long tally = solve(ranges);
-            for (Long num : numbers) {
+            System.out.println("Sum of invalid IDs: " + tally);
-                System.out.println(num);
-            }
 
         } catch (IOException e) {
             e.printStackTrace();
         }
     }
 
+    // Solve by generating only repeated IDs
+    public static long solve(List<long[]> ranges) {
+        long sum = 0;
+
+        for (long[] range : ranges) {
+            long start = range[0];
+            long end = range[1];
+
+            for (long num = start; num <= end; num++) {
+                String numStr = String.valueOf(num);
+                int len = numStr.length();
+
+                if (len % 2 != 0) continue;
+
+                boolean repeated = false;
+                for (int prefixLen = 1; prefixLen <= len / 2; prefixLen++) {
+                    if (len % prefixLen != 0) continue; // must divide evenly
+
+                    String prefix = numStr.substring(0, prefixLen);
+                    String repeatedNum = prefix + prefix;
+                    if (repeatedNum.equals(numStr)) {
+                        repeated = true;
+                        break;
+                    }
+                }
+
+                if (repeated) sum += num;
+            }
+        }
+
+        return sum;
+    }
+
     public static String readFileAsString(String filePath) throws IOException {
         StringBuilder sb = new StringBuilder();
         try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
             String line;
             while ((line = reader.readLine()) != null) {
-                sb.append(line.trim()); // remove extra spaces/newlines
+                sb.append(line.trim());
             }
         }
         return sb.toString();
     }
 
-    public static List<Long> parseRanges(String input) {
+    public static List<long[]> parseRanges(String input) {
-        List<Long> result = new ArrayList<>();
+        List<long[]> result = new ArrayList<>();
         String[] ranges = input.split(",");
 
         for (String range : ranges) {
-            String[] parts = range.split("-");
+            String[] parts = range.trim().split("-");
             if (parts.length != 2) {
                 throw new IllegalArgumentException("Invalid range: " + range);
             }
             long start = Long.parseLong(parts[0]);
             long end = Long.parseLong(parts[1]);
-            result.add(start);
+            result.add(new long[]{start, end});
-            result.add(end);
         }
 
         return result;
     }
-    
 }