solved 2b

inputs/inputProblem2.txt

@@ -0,0 +1 @@
+9191906840-9191941337,7671-13230,2669677096-2669816099,2-12,229599-392092,48403409-48523311,96763-229430,1919163519-1919240770,74928-96389,638049-668065,34781-73835,736781-819688,831765539-831907263,5615884-5749554,14101091-14196519,7134383-7169141,413340-625418,849755289-849920418,7745350-7815119,16717-26267,4396832-4549887,87161544-87241541,4747436629-4747494891,335-549,867623-929630,53-77,1414-3089,940604-1043283,3444659-3500714,3629-7368,79-129,5488908-5597446,97922755-98097602,182-281,8336644992-8336729448,24-47,613-1077

src/Problem1.java

@@ -1,3 +1,5 @@
+package src;
+
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.util.ArrayList;

src/Problem1b.java

@@ -1,3 +1,5 @@
+package src;
+
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.util.ArrayList;

src/Problem2.java

@@ -0,0 +1,85 @@
+package src;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+public class Problem2 {
+
+    public static void main(String[] args) {
+        String filePath = "inputs/inputProblem2.txt";
+
+        try {
+            String input = readFileAsString(filePath);
+            List<long[]> ranges = parseRanges(input);
+            long tally = solve(ranges);
+            System.out.println("Sum of invalid IDs: " + tally);
+
+        } 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());
+            }
+        }
+        return sb.toString();
+    }
+
+    public static List<long[]> parseRanges(String input) {
+        List<long[]> result = new ArrayList<>();
+        String[] ranges = input.split(",");
+
+        for (String range : ranges) {
+            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(new long[]{start, end});
+        }
+
+        return result;
+    }
+}

src/Problem2b.java

@@ -0,0 +1,87 @@
+package src;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+public class Problem2b {
+
+    public static void main(String[] args) {
+        String filePath = "inputs/inputProblem2.txt";
+
+        try {
+            String input = readFileAsString(filePath);
+            List<long[]> ranges = parseRanges(input);
+            long tally = solve(ranges);
+            System.out.println("Sum of invalid IDs: " + tally);
+
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+    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();
+
+                boolean repeated = false;
+
+                for (int prefixLen = 1; prefixLen <= len / 2; prefixLen++) {
+                    if (len % prefixLen != 0) continue;
+
+                    String prefix = numStr.substring(0, prefixLen);
+                    int times = len / prefixLen;
+                    StringBuilder sb = new StringBuilder();
+                    for (int t = 0; t < times; t++) {
+                        sb.append(prefix);
+                    }
+
+                    if (sb.toString().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());
+            }
+        }
+        return sb.toString();
+    }
+
+    public static List<long[]> parseRanges(String input) {
+        List<long[]> result = new ArrayList<>();
+        String[] ranges = input.split(",");
+
+        for (String range : ranges) {
+            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(new long[]{start, end});
+        }
+
+        return result;
+    }
+}