solved 3b

src/Problem3b.java

@@ -0,0 +1,39 @@
+package src;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+
+public class Problem3b {
+
+    public static void main(String[] args) {
+        String filePath = "inputs/inputProblem3.txt";
+        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
+            String line;
+            long total = 0;
+            while ((line = reader.readLine()) != null) {
+                String maxDigits = maxKDigitsString(line, 12);
+                total += Long.parseLong(maxDigits);
+            }
+            System.out.println("Total maximum joltage: " + total);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public static String maxKDigitsString(String digits, int k) {
+        int n = digits.length();
+        char[] stack = new char[k];
+        int top = 0;
+        for (int i = 0; i < n; i++) {
+            char c = digits.charAt(i);
+            while (top > 0 && stack[top - 1] < c && (top - 1 + (n - i)) >= k) {
+                top--;
+            }
+            if (top < k) {
+                stack[top++] = c;
+            }
+        }
+        return new String(stack, 0, k);
+    }
+}