Merge pull request #10 from code-for-tomorrow/exercises

Exercises for Ch. 10-11

Author: phrdang

src/com/codefortomorrow/intermediate/chapter10/practice/RandomNumbers.java

@@ -18,8 +18,10 @@ To call the method, type randInt(7, 77) and assign it to
 and min to Integer.MAX_VALUE when you first initialize them.
 This ensures that when you iterate through the
 randomly generated numbers in your array, the max and min
-are updated correctly.
-(You can also set max to 6 and min to 78.)
+are updated correctly. (You can also set max to 6 and min to 78.)
+
+Note: Interested in seeing how the randInt() method works? You can read
+this Stack Overflow response: https://bit.ly/38IkeY2
 */
 
 public class RandomNumbers {
@@ -33,8 +35,7 @@ public static void main(String[] args) {
      * in the range [min, max]
      * @param min  minimum random integer
      * @param max  maximum random integer
-     * @return a random integer in the range
-     * [min, max]
+     * @return a random integer in the range [min, max]
      */
     public static int randInt(int min, int max) {
         return min + (int) (Math.random() * ((max - min) + 1));

src/com/codefortomorrow/intermediate/chapter10/solutions/RandomNumbers.java

@@ -18,8 +18,10 @@ To call the method, type randInt(7, 77) and assign it to
 and min to Integer.MAX_VALUE when you first initialize them.
 This ensures that when you iterate through the
 randomly generated numbers in your array, the max and min
-are updated correctly.
-(You can also set max to 6 and min to 78.)
+are updated correctly. (You can also set max to 6 and min to 78.)
+
+Note: Interested in seeing how the randInt() method works? You can read
+this Stack Overflow response: https://bit.ly/38IkeY2
 */
 
 public class RandomNumbers {
@@ -67,8 +69,7 @@ public static void main(String[] args) {
      * in the range [min, max]
      * @param min  minimum random integer
      * @param max  maximum random integer
-     * @return a random integer in the range
-     * [min, max]
+     * @return a random integer in the range [min, max]
      */
     public static int randInt(int min, int max) {
         return min + (int) (Math.random() * ((max - min) + 1));

src/com/codefortomorrow/intermediate/chapter11/practice/Average.java

@@ -1,16 +1,23 @@
 package com.codefortomorrow.intermediate.chapter11.practice;
 
+/*
+Code a method called average that takes
+two double parameters, a and b.
+The method should return the average
+of the two doubles.
+
+Test if your average method works in the
+main method by calling it at least 3 times
+with different arguments and printing the results.
+
+Bonus points if you write a JavaDoc comment for
+the average() method.
+*/
+
 public class Average {
 
-    /**
-     * Difficulty: 1
-     *
-     * Returns the average of two doubles
-     * @param a the first double
-     * @param b the second double
-     * @return average
-     */
-    public static double average(double a, double b) {
-        return 0.0; // TODO: Fix!
+    public static void main(String[] args) {
+        // Test your average method here
     }
+    // Write your average method here
 }

src/com/codefortomorrow/intermediate/chapter11/practice/CheckPassword.java

@@ -0,0 +1,47 @@
+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Some websites impose certain rules for passwords.
+Write a method that checks whether a string is a valid password.
+
+Suppose the password rules are as follows:
+■ A password must have at least eight characters.
+■ A password consists of only letters and digits.
+■ A password must contain at least two digits.
+
+Write a program that prompts the user to enter a password and displays
+Valid Password if the rules are followed or Invalid Password otherwise.
+To do this, use a method called isValid which returns true if the password
+is valid and false otherwise.
+
+You may also find it helpful to write a method called
+isAlphanumeric which returns true if the given string
+is only made up of letters and digits.
+
+You may also find it helpful to write a method called
+getNumberOfDigits which returns the number of digits
+in a given string.
+
+You may also find it helpful to use the Character.isDigit(char)
+and Character.isDigit(char) methods. You can read more about them here:
+https://www.tutorialspoint.com/java/java_characters.htm
+
+If you don't want to use those methods, you can also use regular
+expressions (aka regex) and the matches(regex) String method.
+You can read about that here:
+https://www.tutorialspoint.com/java/java_string_matches.htm
+https://www.vogella.com/tutorials/JavaRegularExpressions/article.html
+
+Bonus points for writing JavaDoc comments for the methods.
+
+Adapted from Exercise 6.18, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class CheckPassword {
+
+    public static void main(String[] args) {
+        // test checkPassword method here
+    }
+    // write checkPassword method here
+}

src/com/codefortomorrow/intermediate/chapter11/practice/CreditCard.java

@@ -0,0 +1,139 @@
+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Credit card numbers follow certain patterns. A credit card number
+must have between 13 and 16 digits. It must start with:
+■ 4 for Visa cards
+■ 5 for Master cards
+■ 37 for American Express cards
+■ 6 for Discover cards
+
+In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card
+numbers. The algorithm is useful to determine whether a card number is entered
+correctly or whether a credit card is scanned correctly by a scanner. Credit card
+numbers are generated following this validity check, commonly known as the
+Luhn check or the Mod 10 check, which can be described as follows
+(for illustration, consider the card number 4388576018402626):
+
+1. Double every second digit from right to left. If doubling of a digit results in a
+two-digit number, add up the two digits to get a single-digit number.
+4388576018402626
+2 * 2 = 4
+2 * 2 = 4
+4 * 2 = 8
+1 * 2 = 2
+6 * 2 = 12 (1 + 2 = 3)
+5 * 2 = 10 (1 + 0 = 1)
+8 * 2 = 16 (1 + 6 = 7)
+4 * 2 = 8
+
+2. Now add all single-digit numbers from Step 1.
+4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37
+
+3. Add all digits in the odd places from right to left in the card number.
+6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38
+
+4. Sum the results from Step 2 and Step 3.
+37 + 38 = 75
+
+5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise,
+it is invalid. For example, the number 4388576018402626 is invalid, but the
+number 4388576018410707 is valid.
+
+Write a program that prompts the user to enter a credit card number as a long
+integer. Display whether the number is valid or invalid. Design your program to
+use the following methods:
+
+Returns true if the card number is valid
+public static boolean isValid(long number)
+
+Gets the result from Step 2
+public static int sumOfDoubleEvenPlace(long number)
+
+Returns this number if it is a single digit, otherwise,
+return the sum of the two digits
+public static int getDigit(int number)
+
+Returns sum of odd-place digits in number
+public static int sumOfOddPlace(long number)
+
+Returns true if the digit d is a prefix for number
+public static boolean prefixMatched(long number, int d)
+
+Returns the number of digits in d
+public static int getSize(long d)
+
+Returns the first k number of digits from number. If the
+number of digits in number is less than k, return number.
+public static long getPrefix(long number, int k)
+
+Here are sample runs of the program:
+
+Enter a credit card number: 4388576018410707
+4388576018410707 is valid
+
+Enter a credit card number: 4388576018402626
+4388576018402626 is invalid
+
+Bonus points if you can also print to the user
+what type of card the number is, and for writing JavaDoc comments.
+
+Note: If you need more card numbers to test, you can look here:
+https://www.simplify.com/commerce/docs/testing/test-card-numbers
+(or simply search "test credit card numbers" on Google).
+
+Note: The practice template has method stubs written for you.
+Simply delete the default return values and start coding!
+
+Adapted from Exercise 6.31, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class CreditCard {
+
+    public static void main(String[] args) {
+        // write code here
+    }
+
+    /** Returns true if the card number is valid */
+    public static boolean isValid(long number) {
+        return false;
+    }
+
+    /** Returns the sum of the doubled even-place digits, from right to left */
+    public static int sumOfDoubleEvenPlace(long number) {
+        return 0;
+    }
+
+    /**
+     * Returns the given number if it is a single digit,
+     * otherwise return the sum of the two digits
+     */
+    public static int getDigit(int n) {
+        return 0;
+    }
+
+    /** Returns the sum of the odd-place digits, from right to left */
+    public static int sumOfOddPlace(long number) {
+        return 0;
+    }
+
+    /** Return true if d is a prefix for a number */
+    public static boolean prefixMatched(long number, int d) {
+        return false;
+    }
+
+    /** Returns the number of digits in the given number */
+    public static int getSize(long number) {
+        return 0;
+    }
+
+    /**
+     * Returns the first k number of digits from number.
+     * If the number of digits in number is less than k,
+     * returns number.
+     */
+    public static long getPrefix(long number, int k) {
+        return 0;
+    }
+}

src/com/codefortomorrow/intermediate/chapter11/practice/IsPrime.java

@@ -0,0 +1,21 @@
+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Write a method called isPrime which returns
+true if the given integer is prime and false otherwise.
+Bonus points for writing JavaDoc comments for the method.
+
+Test your isPrime method in the main method by
+calling it at least 3 times and printing the result.
+
+Solution from Listing 6.7, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class IsPrime {
+
+    public static void main(String[] args) {
+        // test isPrime method here
+    }
+    // write isPrime method here
+}

src/com/codefortomorrow/intermediate/chapter11/practice/PrintEvens.java

@@ -1,15 +1,21 @@
 package com.codefortomorrow.intermediate.chapter11.practice;
 
+/*
+Code a method printEvens that takes an integer parameter n.
+The method should print the first n even numbers to the console.
+(Note that 0 is considered an even number.)
+
+Test if your printEvens method works in the main method
+by calling it at least 3 times with different arguments.
+
+Bonus points if you write a JavaDoc comment
+for the printEvens method.
+*/
+
 public class PrintEvens {
 
-    /**
-     * Difficulty: 1
-     *
-     * Print the first n even integers
-     * (consider 0 an even number)
-     * @param n number of even integers to print
-     */
-    public static void printEvens(int n) {
-        // write code here
+    public static void main(String[] args) {
+        // Test your printEvens method here
     }
+    // Write your printEvens method here
 }

src/com/codefortomorrow/intermediate/chapter11/practice/SumDigits.java

@@ -0,0 +1,34 @@
+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Write a method that computes the sum of the digits
+in an integer. Use the following method header:
+
+public static int sumDigits(long n)
+
+For example, sumDigits(234) returns 9 (because 2 + 3 + 4). 
+
+Hint: Use the % operator to extract digits,
+and the / operator to remove the extracted digit.
+For instance, to extract 4 from 234, use 234 % 10 (= 4).
+To remove 4 from 234, use 234 / 10 (= 23).
+
+Use a loop to repeatedly extract and remove the digit
+until all the digits are extracted.
+
+Write a test program that prompts the user to enter an integer and
+displays the sum of all its digits.
+
+Bonus points for writing a JavaDoc comment for the sumDigits method.
+
+Adapted from Exercise 6.2, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class SumDigits {
+
+    public static void main(String[] args) {
+        // test sumDigits here
+    }
+    // write sumDigits method here
+}

src/com/codefortomorrow/intermediate/chapter11/practice/Temperature.java

@@ -0,0 +1,33 @@
+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Write a class that contains the following two methods:
+
+Convert from Celsius to Fahrenheit
+public static double celsiusToFahrenheit(double celsius)
+
+Convert from Fahrenheit to Celsius
+public static double fahrenheitToCelsius(double fahrenheit)
+
+The formula for the conversion is:
+fahrenheit = (9.0 / 5) * celsius + 32
+celsius = (5.0 / 9) * (fahrenheit – 32)
+
+Bonus points for writing JavaDoc comments for both methods.
+
+Write a test program that asks the user for a temperature
+in Fahrenheit and prints out the Celsius conversion. Then
+ask the user for a temperature in Celsius and print out
+the Fahrenheit conversion.
+
+Adapted from Exercise 6.8, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class Temperature {
+
+    public static void main(String[] args) {
+        // Test your methods here
+    }
+    // Write your methods here
+}