/* 
Writer: SP
Date: April 1st
References: knowt & Fiveable
Unit 6: Arrays */

Arrays Intro

• Arrays- A data structure that makes it easier to handle similar types of data.

  • It can store whether primitive or reference data types.

  • Arrays are also reference types

Making Arrays

• There are two different ways to make arrays

  • A constructor method vs. A pre-initialized array.

Constructor Method:

dataType[] arrayName = new dataType[numberOfItems];

• To make an array that hold 10 items, it will be: int[] Array = new int[10];

• Default value of array

  Datatype	Default Value
  int	0
  double	0
  boolean	false
  reference	null

Pre-initialized Arrays:

int[] arrayOne = {1,2,3,4,5,6};

• We initialized an array of 6 integers.

Accessing elements

• code to access elements: arrayName[index]

• Java is a zero-indexed language, thus its index starts at 0.

• To define the length of array, we use arrayName.length.

  • It is not index thingy, so it will return the correct number.

  • Want to access the last element using .length, you should write: ;

    • arrayName.length - 1

• ArrayIndexOutOfBoundsException:

  • When we use an index outside the allowed range.

Traversing Arrays:

• To access every value in the array.

1. Basic Traversing

// Traversing all elements using for loop and start at index 0. 

int[] list = new int[5];
for (int i = 0; i < list.length; i++) {
   condition;
}

// Traversing all elements using while loop and start at index 0. 

int[] list = new int[5];
int i = 0;

while (i<list.length) {
   condition;
   i++;
}

2. Reverse Traversing

int[] arr = new int[5];
for (int i = arr.length-1; i<=0; i—-) {
   condition;
}

int index = arr.length-1;
while (index<=0) { 
   condition;
   i—-;
}

Enhanced For Loop

• Enhanced for loop can be used to traverse through most data structures.

  • It cannot reverse.

• Structure:

for (dataType i : arrayName) { 
   do something with i;
}

• We cannot directly change the value of elements using enhanced for loop because ‘i’ is just copy of element in the array.

• However, we can use mutator methods to set the value.

/** Represents a student
*/
public class Student {
  private String name;
  
  /** Sets the name of the Student
  */
  public void setName(String name) {
    this.name = name;
  }

  /** Other instance variables, methods, and constructors not shown
  */
}
// IN ANOTHER CLASS
/** Resets all students' names
*/
public static void doubleArray(Student[] array, String defaultName) {
  for (Student student: array) {
    student.setName(defaultName); // Sets each student's name to a default name
  }
}

Developing Algorithms

0. Reverse the array

public class ReverseArray {
    public static void main(String[] args) {
        // Initializing an array
        int[] originalArray = {1, 2, 3, 4, 5};
        int length = originalArray.length;

        // Printing the original array
        System.out.println("Original Array:");
        for (int i = 0; i < length; i++) {
            System.out.print(originalArray[i] + " ");
        }

        // Reversing the array
        for (int i = 0; i < length / 2; i++) {
            int temp = originalArray[i];
            originalArray[i] = originalArray[length - 1 - i];
            originalArray[length - 1 - i] = temp;
        }

        // Printing the reversed array
        System.out.println("\nReversed Array:");
        for (int i = 0; i < length; i++) {
            System.out.print(originalArray[i] + " ");
        }
    }
}

1. Finding Max in array of double values (Comparing with the first index value):

private double findMax(double[] v) {
   double max = v[0];
   for (int i = 1; index < v.length; i++) {
      if (v[i] > max) {
         max = v[i];
      }
   }
   return max
}

2. Finding Min value in int array (Comparing with the absolute maximum value):

private int findMin(int[] v) { 
   int min = Integer.MAX_VALUE;
   for (int currentValue : v) { 
	if (currentValue < min) { 
	   min  = currentValue;
	}
   }
   return min;
}

3. Calculate the average value of array

private double findMean(double[] list) { 
   double sum = 0.0;
   for (int i : list) { 
      sum += i;
   }
   double mean = sum/list.length;
   return mean;
}

4. Doing a right shift.

5. Left Shift

6. Finding Duplicate

for (int x = 0; x < Array.length; x++) { 
  for (int y = 0; y< Array.length; y++) { 
    if (array[x] == array[x] && x!=y) { 
      // Duplicate statement
    }
  }
}