Introduction To Java and Programming Fundamentals

Solutions to all sample problems on HackerRank under the Java domain can be looked up here.

Programming is a very hands process and is both an art as well as a science. We are engineers and are required to create efficient solutions but at the same time our programs should be highly readable and flexible and all the other snappy terms which makes it an art as well.

To become proficient in this art, there are many resources, and books and tutorials. Each has it's merit and making the first step in any direction is commendable, but the cardinal factor at the end of the day will be you sitting down (or standing) and writing code. No book or resource can substitute that.

So, what are you waiting for 😀😉 - try as many questions (below or otherwise) as you can....

Day 1

Topics Covered

• Java Introduction
• Printing values and Taking input
• Variables and Data Types
• Operators and Arithmetic
• Conditional Statements
• Comments
• Import Statements

Sample Problems To Try

Problem	Source	Solution Link
Welcome to Java	HackerRank	Solution
Java StdIn and StdOut I	HackerRank	Solution
Java If Else	HackerRank	Solution
Data Types Problem	HackerRank	Solution
Java Int To String	HackerRank	Solution
Java Currency Formatter Problem	HackerRank	Solution
Java String Reverse	HackerRank	Solution

Day 2

Topics Covered

• While Loop
• For Loop
• Break Statement
• Fibonacci Series

Sample Problems To Try

Problem	Source	Solution Link
Java Output Formatting	HackerRank	Solution
Java Strings Introduction	HackerRank	Solution
Java Substring	HackerRank	Solution
Java String Compare	HackerRank	Solution
Java Date and Time	HackerRank	Solution

Loop based & Pattern based questions given here

Problem No.	Solution
Question 1	Solution
Question 2	Solution
Question 3	Solution
Question 4	Solution
Question 5	Solution
Question 6	Solution
Question 7	Solution
Question 8	Solution
Question 9	Solution
Question 10	Solution
Question 11	Solution
Question 12	Solution
Question 13	Solution
Question 14	Solution
Question 15	Solution
Question 16	Solution
Question 17	Solution
Question 19	Solution

Day 3

Topics Covered

• For Loop
• Nested For Loops
• Pattern Printing Questions

Sample Problems to Try

• Question 18 of the loops section of begin with java.

Problem	Solution Link
Question 18. a	Solution
Question 18. b	Solution
Question 18. c	Solution
Question 18. d	Solution
Question 18. e	Solution
Question 18. f	Solution

• WAP (Write a program) to a print the following pattern. User enters rows [See Solution]

********
***  ***
**    **
*      *
        
*      *
**    **
***  ***
********

• WAP to print the following pattern. User will enter number of rows (rows >= 2). If user enters rows < 2 then no pattern is printed. You can also add a second variable called columns that takes how many stars * to print in the first and last line. [See Solution]

********
*      *
*      *
*      *
*      *
********

• WAP to print the following pattern, User enters rows [See Solution]

*****
*  *
* *
*

• WAP to print the following pattern. User enters rows. [See Solution]

* * * * *
 * * * *
  * * *
   * *
    *

• WAP to print the following pattern. User enters rows. [See Solution]

    *
   * *
  * * *
 * * * *
* * * * *

• WAP to print the following pattern. User enters rows. [See Solution]

    *
   * *
  *   *
 *     *
* * * * *

• WAP to print the following pattern. User enters rows. [See Solution]

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

• WAP to print the following pattern. User enters rows. [See Solution]

1 2 3 4 5
1 2 3 4
1 2 3
1 2
1

• WAP to print the following pattern. User enters rows. [See Solution]

1
1 2
1 x 3
1 x x 4
1 x x x 5
1 2 3 4 5 6

• WAP to print the following pattern. User enters rows. [See Solution]

A
A B A
A B C B A
A B C D C B A

• WAP to print the following patter. User enters rows. [See Solution]

********1********
*******2*2*******
******3*3*3******
*****4*4*4*4*****
****5*5*5*5*5****
***6*6*6*6*6*6***
**7*7*7*7*7*7*7**
*8*8*8*8*8*8*8*8*

• WAP to print the following patter. User enters rows. [See Solution]

   *
  * *
 * * *
  * *
   *

• WAP to print the following pattern. User enters rows. [See Solution]

    *
   * *
  *   *
 *     *
*       *
 *     *
  *   *
   * *
    *

• WAP to print the following pattern. User enters rows. [See Solution]

*
**
***
****
***
**
*

In case rows = 4

*
**
**
*

• WAP to print the following pattern. User enters rows. [See Solution]

For row = 3

3
44
555
6666
555
44
3

For row = 2

2
33
444
33
2

For row=5

5
66
777
8888
99999
101010101010
99999
8888
777
66
5

• WAP to print the following pattern. User enters rows. [See Solution]

For rows = 4.

1
2 3
4 5 6
7 8 9 10

For row = 2

1 
2 3

• WAP to print the following pattern. User enters rows. For rows = 3 [See Solution]

1
2*3
4*5*6
4*5*6
2*3
1

for row = 4

1
2*3
4*5*6
7*8*9*10
7*8*9*10
4*5*6
2*3
1

• WAP to print the following pattern (Pascal's Triangle). User enters rows. [See Solution]

For rows = 5

1
1 1
1 2 1
1 3 3 1
1 4 6 4 1

The pattern is derived in the pascal's triangle using values in the previous row. e.g.

1
1 1
1 (1 + 1) 1
1 (1 + 2) (2 + 1) 1
1 (1 + 3) (3 + 3) (3 + 1) 1

• WAP to print the following pattern (Hollow Rhombus). [See Solution]

For row=3

******
**  **
*    *
*    *
**  **
******

For row = 5

**********
****  ****
***    ***
**      **
*        *
*        *
**      **
***    ***
**** *****
**********

• WAP to print the following pattern (Butterfly pattern). [See Solution]

For row = 3

*    *
**  **
******
******
**  **
*    *

For row = 5

*        *
**      **
***    ***
****  ****
**********
**********
****  ****
***    ***
**      **
*        *

Day 4

Topics Covered

• Switch Statement
• Amortised Code Analysis (Big-O Notation)
• Functions
• java.Math Module

Sample Problems

• Time Complexity Problems [InterviewBit]
• WAP to create a function add() that takes 2 integer values and returns the sum.

public static int add(int a, int b) {
}

• WAP to create a function difference() that takes 2 integer values and returns the difference.

public static int difference(int a, int b) {
}

• WAP to create a function product() that takes 2 integer values and returns the product.

public static int product(int a, int b) {
}

• WAP to create a function divide() that takes 2 integer values and returns the quotient.

public static int divide(int a, int b) {
}

• WAP that creates a function which calculates the factorial of a number n. Where:

0! = 1
1! = 1
3! = 1 * 2 * 3 = 6
5! = 1 * 2 * 3 * 4 * 5 = 120

• WAP to create a function that calculates the Binomial Coefficient nCr. Where:

nCr = n! / (r! * (n-r)!)
4C0 = 4! / 0! 4! = 1
3C2 = 3! / 2!*1! = 6 / 2 = 3

• WAP to create a function that calculates the Permutation value nPr. Where

nPr = n! / (n-r)!
5P0 = 5! / 5! = 1
6P3 = 6! / 3! = 6*5*4 = 120

• WAP to create a function to check whether a given number is prime or not.

private static boolean isPrime(int number) {
} 

• WAP to create a function that returns the length of a hypotenuse of a right angle triangle given the lengths of the other 2 sides

private static double hypotenuseLength(double a, double b) {
}

• WAP to create a function to return the day of the week (name) from the day number. Example

private static String dayFrom(int value) {
}

dayFrom(0) --> "Sunday"
dayFrom(1) --> "Monday"
...
...
dayFrom(6) --> "Saturday"

Day 5

Topics Covered

• Functions and methods continued
• Function Polymorphism
• Method Overriding
• Recursion

Sample Problems

• WAP to return the value of the sum of the following series recursively given n. [See Solution]

  1^1 + 2^2 + 3^3 + 4^4 + ... + n^n 
  

• WAP a program that returns that sum of the first N natural numbers and finds this sum recursively. [See Solution]

  f(N) = 1 + 2 + 3 + ... + N   
  

  so, for N = 3 f(3) = 1 + 2 + 3 = 6 and for N = 5 f(5) = 15.

• WAP a program that calculates the sum of the series

  f(N) = 1 + 2^2 + 3^2 + ... + N^2
  

  using a recursive function. [See Solution]

Day 6

Topics Covered

• 1D Arrays
• Varargs Methods
• Foreach Loop
• 2D Arrays

Sample Problems

1. WAP to input an integer number length from the user and then instantiate an integer array of size length and then display that array on the terminal with all entered values.
   [See Solution]

2. WAP that inputs an integer array from the user and returns the sum of all its elements. Create a dedicated method for calculating array sum with the following signature. [See Solution]

   private static int sum(int[] array);

3. WAP that inputs an integer array from the user and prints the number of even, odd and zero elements. [See Solution]

4. WAP to implement linear searching in an array. The user enters an array of size n and then an integer element. search for this element in the array and return the first index at which it is found otherwise return -1 if not found in the array. [See Solution]

5. WAP that takes an array from the user and returns a reverse array with the order of all elements reversed and then prints this reversed array. [See Solution]

   If the input array is array = [1, 2, 3, 4, 5] then the resultant array should be = [5, 4, 3, 2, 1]
   

   The method should have the following signature.

    private static int[] reverse(int[] array);

6. WAP that takes an integer array from the user and returns the product of all it's elements. [See Solution] The method signature should be

   private static long product(int[] array);

7. WAP to tell whether an array is an anagram or not. The user will enter an integer array. [See Solution] For example

   array = [1, 2, 1] this is an anagram as the reverse of this array is also [1, 2, 1]
   array = [1, 1, 1, 1] This is also an anagram as the reverse is the same [1, 1, 1, 1]
   array = [] The empty array is also an anagram as the reverse is [] the same.
   array  = [-1, 0] is not an aanagram as the reverse = [0, -1] isn't the same.
   

   Crete a method with the following signature that returns boolean; true or false i it is an anagram or not.

    private static boolean isAnagram(int[] array);

8. WAP to Merge 2 sorted arrays and return the new array which is also sorted. [See Solution] For example

   Let there be 2 arrays first = [1, 10, 20] and second = [1, 2, 4, 10, 67] Define a function with 
   a sigature as:
   

    private static int[] merge(int[] first, int[] second);

    which should return an array = [1, 1, 2, 4, 10, 10, 20, 67]
   

Day 7

Topics Discussed

• Object Oriented Programming Basics
• Classes and Objects
• Constructors
• Default Constructors
• Parameterized Constructors
• Constructor Overloading
• Access Modifier
• The Final Keyword

Sample Problems

Problem	Platform	Solution Link
Java Inheritance I	HackerRank	Solution
Java Inheritance II	HackerRank	Solution
Java Abstract Class	HackerRank	Solution
Java Interface	HackerRank	Solution
Java Method Overriding	HackerRank	Solution
Java Overriding II (Super Keyword)	HackerRank	Solution

Day 8

Topics Covered

• OOP Continued
• Class Inheritance
• The Java Object Class
• Java Interfaces
• Dynamic Binding
• The Java Collection Interface
• The Java ArrayList Class
• Example ArrayList
• Example HashSet

Sample Problems

Try the problems given below and have a look at the solution only after you have solved it to see the different implementations and ideas we might've used or to use as a reference if unable to solve yourself.

Problem	Platform	Solution Link
Java List	HackerRank	Solution
Java ArrayList	HackerRank	Solution
Java Comparator	HackerRank	Solution
Covariant Return Types	HackerRank	Solution

Day 9

Topics Discussed

• @Override decorator
• Overriding toString() and equals() method from the java.lang.Object Object
• Collections Interface
• List Interface
• Arraylist class
• Stack Class
• Queue Interface
• LinkedList Class
• Priority Queue
• Iterable Interface
• Iterators
• Comparator Interface
• compareTo() method

Sample Problems

Try the problems given below and have a look at the solution only after you have solved it to see the different implementations and ideas we might've used or to use as a reference if unable to solve yourself.

Problem	Platform	Solution Link
Java Stack	HackerRank	Solution
Java Priority Queue	HackerRank	Solution
Maximum Element	HackerRank	Solution
Equal Stacks	HackerRank	Solution
Balanced Brackets	HackerRank	Solution

Day 10

Topics Discussed

Sample Problems

Problem	Platform	Solution Link
Java Anagrams	HackerRank	Solution
Java Hashset	HackerRank	Solution
Java Map	HackerRank	Solution
Pair Sums	HackerRank	Solution