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1D Array - 2

Agenda

  1. Revision
  2. Implement Function
  3. Increasing Order [increasing and non-decreasing]
  4. Drawbacks of Array
  5. Right shift of the array
  6. Array List introduction
  7. Functions [add, get, set, remove, size, sort]
  8. ArrayList functions via code
  9. Write a function which takes arrayList as input and update all values by 1
  10. Return an arraylist with all even numbers

Revision

Let us revise what we discussed in the last class wit the help of quizzes.

Question

What will be output for this program ? 

int[] myArray = {1, 2, 3, 4, 5};
System.out.println(myArray[2]);

Choices

  • 2
  • 3
  • 4

Question

What will be output for this program ?

int[] myArray = new int[3];
System.out.println(myArray[1]);

Choices

  • 0
  • Null
  • Error

Question

What will be output for this program ? 

int[] myArray = {1, 2, 3, 4, 5};
System.out.println(myArray.length);

Choices

  • 4
  • 0
  • 5

Question

What will be output for this program ? 

int[] myArray = {1, 2, 3, 4, 5};
myArray[2] = 6;
System.out.println(myArray[2]);

Choices

  • 6
  • 3
  • 3
  • Error

Return arr[] Syntax

Implement Function

Given N, create an array of size N, which should contain all elements in increasing order from 1 to N.

Example

N = 3
arr[3] = { 1, 2, 3 }

N = 5
arr[5] = { 1, 2, 3, 4, 5 }

Question

Given N = 6, create an array of size N containing all elements in increasing order from 1 to N.

Choices

  • 0 1 2 3 4 5 6
  • 1 2 3 4 5 6
  • 6 5 4 3 2 1

Implement Function Code

Pseudocode

static int[] num(int N){
    int arr = new int[N];
    for(int i = 0; i < N; i++){
        arr[i] = i + 1;
    }
    return arr;
}

Increasing Order

Numbers arranged from smallest to largest. Note: If elements are equal then no issues

Scritly Increasing Order

Arrangement of numbers such that the next number is always greater than the previous number.

Question

Check whether the given numbers are in increasing order?

3, 4, 4, 4, 4, 5, 5, 7, 9, 18, 18, 26

Choices

  • yes
  • no
  • maybe

Question

Check whether the given numbers are in increasing order?

-1, -2, -3, -4, -5

Choices

  • Yes
  • No
  • Maybe

Question

Check whether the given numbers are in strictly increasing order?

3, 9, 16, 24, 29, 29, 34, 50

Choices

  • Yes
  • No
  • Maybe

Checking Strictly Increasing Array

Given an integer N, create an array of size N containing elements in increasing order from 1 to N. Check if the created array is strictly increasing (each element is greater than the previous element).

Example

For N = 5, the array arr will be {1, 2, 3, 4, 5}, and it is strictly increasing.

For N = 5, the array arr will be {1, 2, 2, 4, 5}, and it is not strictly increasing.

Question

Check whether the given numbers are in strictly increasing order?

21, 39, 46, 97, 105

Choices

  • Yes
  • No
  • Maybe

If Array Is Strictly Increasing Code

Note to instructor: Explain logic of implementing this in code format here

Pseudocode

static boolean isStrictlyIncreasing(int N) {
    int[] arr = new int[N];
    for (int i = 0; i < N; i++) {
        arr[i] = i + 1;
    }

    for (int i = 1; i < N; i++) {
        if (arr[i] < arr[i - 1]) {
            return false; // Array is not strictly increasing
        }
    }

    return true; // Array is strictly increasing
}

Right Shift of An Array

Given an array of size N, shift all the elements to the right by 1 and move the last element to the beginning of array

Example 1

N = 10
arr[10] = { 7, 4, 9, 11, 2, 24, -5, 17, 1, 8 }
Ans =
arr[10] = { 8, 7, 4, 9, 11, 2, 24, -5, 17, 1}

Question

Right shift the given array

arr[] = {10, 20, 30, 40, 50, 60}

Choices

  • 60, 50, 40, 30, 20, 10
  • 0, 10, 20, 30, 40, 50, 60
  • 60, 10, 20, 30, 40, 50

Right Shift of An Array Idea and Code

Idea

  1. Store last element of original array in a temp variable for future use (temp = arr[n - 1])
  2. Traverse from end to first index and do arr[i] = arr[i - 1]
  3. Till here all indexes are updated with their new value except 0th index. Finally do
    arr[0] = temp

Pseudocode

static int[] rotateByone(int arr[]){
    int n = arr.length
    int temp = arr[n - 1]
    for(int i = n - 1; i >= 1; i--){
        arr[i] = arr[i - 1]
    }
    arr[0] = temp;
    return ans;
}

Drawbacks of Arrays

Once array size is fixed, it cannot be changed.

If we want to change, we need to create a new array.

int[] ar=new int[4];

This can only store 4 elements, if we want to store 1 more element we cannot update the size. We have to create a new array only.

Arraylist

Definition

ArrayList is a class that provides a resizable array implementation that is similar to an ordinary array, but with the added benefit of being able to resize dynamically as elements are added or removed. An ArrayList can store objects of any type, including primitives.

Syntax

The general syntax for creating an ArrayList in Java is as follows:

ArrayList<DataType> listName = new ArrayList<DataType>();
where -

  • DataType is the data type of the elements that will be stored in the list (e.g. Integer, String, Object).
  • listName is the name given to the ArrayList object.

Note: There is no need to mention size in Arraylist, an empty Arraylist is created.

Example

Here's an example that creates an ArrayList of integers and adds the values 10, 20, 30, and 50 to it:

// Create an ArrayList of integers
ArrayList<Integer> al = new ArrayList<>(); // size = 0

// Add integers to the list
al.add(10); // size = 1
al.add(20); // size = 2
al.add(30); // size = 3
al.add(50); // size = 4

Some Methods in Arraylist

  • Adding an element at the end -

We can add an element at the end of Arraylist using the add(value) method:

al.add(10)

Task: Find out how to add a new value at a particluar index in an ArrayList.

  • Total elements -

We can get the size of the Arraylist using the size() method:

int n = al.size(); // Returns the number of elements in the list
  • Access ith index element of an Arraylist -

We can access ith index element of an Arraylist using the get(index) method:

int element = al.get(2); // Returns the element at second index

Question

ArrayList<Integer> al = new ArrayList<>();
al.add(10);
al.add(20);
al.add(30);
al.add(40);
System.out.print(al.get(2));

Choices

  • 10
  • 20
  • 30
  • 40
  • Error

Explanation:

We first created an empty arraylist al. We then added 10, 20, 30 & 40 to it, the list becomes al = [10, 20, 30, 40]. The element at 2nd index is 30. Hence, answer is 30.

Question

ArrayList<Integer> al = new ArrayList<>();
al.add(10);
al.add(20);
al.add(30);
al.add(40);
System.out.print(al.get(4));

Choices

  • 40
  • 20
  • Error
  • 10

Explanation:

We first created an empty arraylist al. We then added 10, 20, 30 & 40 to it, the list becomes al = [10, 20, 30, 40]. The size of the array is 4 with indexes from 0 - 3. There is no index 4. Hence, the code gives an error.

ArrayList

  • Update existing element -

We can update the existing element of an Arraylist using the set(index, value) method:

// myList = [10, 20, 30, 50]
myList.set(2, 40); // Updates the element at second index with value 40
// updated myList = [10, 20, 40, 50]

myList.set(6, 60); // Gives error because index 6 does not exist
  • Remove an element -

We can remove an element from the Arraylist using the remove(index) method:

// myList = [10, 20, 40, 50]
myList.remove(2); // Removes the element at 2nd index from array
// updated myList = [10, 40, 50]
  • Sort the arraylist -

We can sort the Arraylist using the Collections.sort(arraylist_name) method:

// myList = [10, 20, 40, 50]
myList.remove(2); // Removes the element at 2nd index from array
// updated myList = [10, 40, 50]

Note: Here is the link to example code snippet for practice.

Question

What will be the output of the following code?

public static void main(String[] args) {
    ArrayList<Integer> ar = new ArrayList<>();
    ar.add(1);
    ar.add(2);
    ar.add(3);

    ar.set(1, 5);
    ar.set(2, ar.get(0) + ar.get(1));

    System.out.println(ar);
}

Choices

  • [1, 5, 3]
  • [1, 7, 3]
  • [1, 5, 6]
  • [1, 6, 3]

Question

Predict the output

public static void main(String[] args) {
    ArrayList<Integer> ar = new ArrayList<>();
    ar.add(-5);
    ar.add(20);
    ar.add(19);
    ar.add(50)

    ar.remove(1);

    System.out.println(ar);
}

Choices

  • [-5, 19, 20]
  • [20, 19, 50]
  • [-5, 20, 50]
  • [-5, 20, 19, 50]

Question

What will be the output?

public static void main(String[] args) {
    ArrayList<Integer> ar = new ArrayList<>();
    ar.add(5);
    ar.add(2);
    ar.add(9);
    ar.add(1);

    Collections.sort(ar);

    System.out.println(ar);
}

Choices

  • [5, 2, 9, 1]
  • [9, 5, 2, 1]
  • [1, 2, 5, 9]
  • [2, 1, 5, 9]

Problem Statement

Write a function which takes arrayList as input and update all values by 1

Example 1

temp : [20, 15, 8, 25, 21]
ans :  [21, 16, 9, 26, 22]

Pseudo Code:

static ArrayList<Integer>  increaseByOne(ArrayList<Integer> al){
        //iterate over the ArrayList
        int n = al.size();

        for(int i = 0; i < n; i++){
            //access ith index element : al.get(i)
            int num = al.get(i);
            al.set(i, num + 1);

        }
        return al;
    }

Problem Statement

Given an ArrayList of integers, return all the even numbers in the ArrayList.

Example 1

Input = 10 13 7 14 16 19 22 9 11
Output = 10 14 16 22

Example 2

Input = 4 9 1 10 22 21 45
Output = 4 10 22

Solution

Iterate on the arrayList and check if element is even. If yes add it to ans arrayList.

Pseudocode

public static ArrayList<Integer> getEvenNumbers(ArrayList<Integer> list) {
    ArrayList<Integer> evenNumbers = new ArrayList<>();

    for (int i = 0; i < list.size(); i++) {
        int num = list.get(i);
        if (num % 2 == 0) {
            evenNumbers.add(num);
        }
    }

    return evenNumbers;
}