13.1.java

public class ArrayMadness {
   public static int findMax(int [] numbersArray) {
      int max = numbersArray[0];
      for (int number : numbersArray) {
         if (number > max) {
            max = number;  
         }
      }
      return max;
   }

   public static int findMin(int [] numbersArray) {
      int min = numbersArray[0];
      for (int number : numbersArray) {
         if (number < min) {
            min = number;  
         }
      }
      return min;
   }

   public static int totalMaxMin(int [] numbersArray) {
      return findMax(numbersArray) + findMin(numbersArray);
   }
  
   public static void main(String[] args) {
      int [] testValues = {6, 20, 31, 2, 7, 14};
                
      if (findMax(testValues) == 31) {
         System.out.println("Part A is correct.");
      }
      else {
         System.out.println("Part A is incorrect.");
      }
      
      if (findMin(testValues) == 2) {
         System.out.println("Part B is correct.");
      }
      else {
         System.out.println("Part B is incorrect.");
      }      
      
      if (totalMaxMin(testValues) == 33) {
         System.out.println("Part C is correct.");
      }
      else {
         System.out.println("Part C is incorrect.");
      }         
   }
}

13.2.java

public class Encrypter { 
   // lowercase letters of the alphabet 
   private char[] normalAlphabet = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
                                    'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
                                    'u', 'v', 'w', 'x', 'y', 'z'};
   private char[] encryptAlphabet = new char[26]; 

   private int shiftAmount;
   private boolean shiftToLeft;

   public Encrypter(int shiftAmount, boolean shiftToLeft) { 
      this.shiftAmount = shiftAmount;
      this.shiftToLeft = shiftToLeft;
      if (shiftToLeft) {
         shiftLeft();
      } else {
         shiftRight();
      }
   } 

   public String encrypt(String normalWord) { 
      String newString = "";
      for (char c : normalWord.toCharArray()) {
         for (int i = 0; i < this.normalAlphabet.length; i++) {
            if (this.normalAlphabet[i] == c) {
               newString += this.encryptAlphabet[i];
               break;
            }
         }
      }
      return newString;
   }
   
   public void shiftLeft() {
      for (int i = 0; i < this.normalAlphabet.length; i++) {
         int newPos = i + this.shiftAmount;
         if (newPos < this.normalAlphabet.length) {
            this.encryptAlphabet[newPos] = this.normalAlphabet[i];  
         } else {
            this.encryptAlphabet[newPos - 26] = this.normalAlphabet[i];  
         }
      }
   }
   
   public void shiftRight() {
      for (int i = 0; i < this.normalAlphabet.length; i++) {
         int newPos = i - this.shiftAmount;
         if (newPos < 0) {
            this.encryptAlphabet[newPos + 26] = this.normalAlphabet[i];  
         } else {
            this.encryptAlphabet[newPos] = this.normalAlphabet[i];  
         }
      }
   }
}

13.3.java

public class NumberChanger {
    public static int [] changeNumbers(int[] numberArray, int changeFrom, int changeTo) {
       for (int i = 0; i < numberArray.length; i++) {
         if (numberArray[i] == changeFrom) {
            numberArray[i] = changeTo;  
         }
       }
       return numberArray;
    }
    
    public static void printArray(int[] numberArray) {
        for (int i : numberArray) {
            System.out.print(i + " ");  
        }
        System.out.println();
    }

   public static void main(String args[]) {
      int [] testArray = {1, 3, 5, 3, 7, 7, 8, 1, 5, 3};
      int [] changedArray = changeNumbers(testArray, 3, 5);

      System.out.println("Expected output: 1 5 5 5 7 7 8 1 5 5");
      System.out.print("Your output: "); 
      printArray(changedArray);
   } 
}

13.4.java

import java.util.ArrayList;

public class Quizzes {
   public int[] getScores(int[] scoresArray, String dayOfWeek){
      String[] daysOfTheWeek = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday"};
      int num = 0;
      int[] ret = new int[scoresArray.length/5];
      for (int i = 0; i < daysOfTheWeek.length; i++) {
         if (daysOfTheWeek[i].equals(dayOfWeek)) {
            num = i;
            break;
         }
      }
      for (int i = 0; i < scoresArray.length/5; i++) {
         ret[i] = scoresArray[(i*5)+num];
      }
      return ret;
   }

   public String bestDay(int[] scoresArray){
      String[] daysOfTheWeek = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday"};
      String best = "";
      double max = 0.0;
      for (String day : daysOfTheWeek) {
         double average = 0.0;
         int[] scores = getScores(scoresArray, day);
         for (double score : scores) {
            average += score;  
         }
         average /= scores.length;
         if (average > max) {
            max = average;
            best = day;
         }
      }
      return best;
   }
}