15-100 Sections U-V-AA / Spring 2009
Midterm Exam #1 (Programming Portion)
Exam Date:  Tue 3-Mar-2009

2 Questions + 1 Bonus Question / 20 Minutes
All questions are equally weighted (10 points each / 20 points total)

Notes:

• These are the same directions as for Quiz 5.
  
  
• On this portion of the midterm, you will use a compiler to write code.
• You may access the course web site, Sun’s online API, and the compiler of your choice.
• You may not access anything else (no notes, books, etc, no Google or other searches, and certainly no code!).
• Place your solutions in a single Java file named Midterm<andrewId>.java
  (So for me it would be Midtermkoz.java)
• When you are done, you should email your solution both as an attachment and pasted into the body of the message. Send it to me (andrew id: koz), and be sure to cc yourself!
  
  
• In your code, you may use loops, conditionals, helper methods, methods from any Java classes in Sun’s library, etc, even arrays if you wish (though they are not required).
• Each problem asks you to write a void method that takes no parameters.
• Your code will only be graded for correctness, not style.
• For efficiency during a quiz, do not use prompts, etc. Just provide the required UI.
• Your code must compute the answers! Hardcoded answers will not receive any credit.
• Do not use web-based scanners for this quiz. Use file-based scanners.
• Thus, before starting this quiz, download this file to your desktop:
  http://kosbie.net/cmu/spring-09/15-100/resources/millionDigitsOfPi.txt
  
  
• To save some time, you should start with this code, which also includes the import statements and the getFileScanner helper method for you.
  
  // <name>, <andrewId>, <section>
  import java.util.*;
  import java.io.*;
  class Midterm {
  public static void main(String[] args) {
  printMostFrequentDigit();
  printOddsOf20OrMore();
  }
  
  public static void printMostFrequentDigit() {
  System.out.println("printMostFrequentDigit not yet written!");
  }
  
  public static void printOddsOf20OrMore() {
  System.out.println("printOddsOf20OrMore not yet written!");
  }
  
  
  // Convenient helper method for reading from a file.
  public static Scanner getFileScanner(String filename) {
  Scanner scanner = null;
  try { scanner = new Scanner(new java.io.File(filename)); }
  catch (Exception e) {
  System.out.println("File not found");
  return null;
  }
  return scanner;
  }
  }
  
  

1. printMostFrequentDigit
Write a method, printMostFrequentDigit, that prints the digit that occurs most frequently in the file. In case of a tie, print all such digits in order from least to greatest.

2. printOddsOf20OrMore
If you roll 5 six-sided dice and add their values, the sum must be between 5 and 30 (right?). Write a method, printOddsOf20OrMore, that uses Monte Carlo methods to compute the odds that this sum is at least 20 or greater. As usual, use enough trials to get a reasonably accurate result. Hint: remember to create only one instance of Random!

3. Bonus/Optional: sort
Write a method that takes an array of int’s and sorts them without calling Arrays.sort. Write a short explanation in a comment as to how your method works.