Thread: How to find maximum, minimum and occurence time of index in an array list

I have been given an exercise to find how many times has a certain index (content value) has been occured as well as the maximum and minimum value index in an array list. For example, if the user inputs the following [10, 10, 20, 20, 30, 40 , 50] and picks the number 20 to see how many times it has occured or listed in an array, it should give an output similar to the following:

10
10
20
20
30
40
50
 
Search for? 20
20 is at index 2
20 is at index 3

1. How can I repeat or make the computer count all the value content of a specific number with their index? I do not know where to begin but here is some of my coding and I have been stuck for a while in this one:

2. After counting a specific value content of an index, how can I identify the maximum and minimum value content of an index without using collections.max or min nor any other methods. In other words, I am trying to find a linear or mathematical solution to the problem please.

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Collections;
 
public class IndexOf {
 
    public static void main(String[] args) 
    {
        Scanner scanner = new Scanner(System.in);
        ArrayList<Integer> arrayList = new ArrayList<>();
 
        while (true) 
        {
            int input = scanner.nextInt();
            if (input == -1) 
            {
                break;
            }
            arrayList.add(input);
        }
        System.out.println("search for? ");
        int input2 = scanner.nextInt();
        System.out.println(input2 + " is at index " + arrayList.indexOf(input2));
 
    }
}

Originally Posted by Norm

If all the numbers have been loaded into a list, can you write code to go through the list and print out its contents?



Then instead of printing the contents, change the code to compare each element in the list against the value to search for.

Yes the code would be: system.out.println(arrayList); after the while loop to list [all the array elements I have inputted], do correct me if I am wrong please.

If I have 5 elements in an array list, why do I have to compare 5 elements against the value that I am searching for? what is the idea behind it?

Originally Posted by Norm

That would show all the elements in one line.
I was asking for code that would show each element on its own line. That was preparing you to write code to compare the elements instead of printing them.


If you have a list and what to find one or more elements in the list, you need to access each one and compare its contents against the desired value.

public class IndexOf {
 
    public static void main(String[] args) 
    {
        Scanner scanner = new Scanner(System.in);
        ArrayList<Integer> arrayList = new ArrayList<>();
        int input;
        while (true) 
        {
            input = scanner.nextInt();
            if (input == -1) 
            {
                break;
            }
            arrayList.add(input);
        }
        System.out.println(arrayList.get(2));
        System.out.println(arrayList.get(3));
 
    }
}

This how to access each and every element, but this is not a practical approach because if I have an array list of 10 to 20 elements, I have to print out many code lines for printing.

As for comparing, I still do not understand what I am comparing elements to the value that I am searching for, do you mean that I am comparing elements to find numbers/elements that are in common with the desired value?

for (int loopValue = 0; loopValue < arrayList.size(); loopValue++) {
            System.out.println(arrayList.get(loopValue));
        }

I believe this is what you were referring to, printing out each and every element individually in each line?

Originally Posted by Norm

Yes, that loop looks at each element in the list one at a time, starting with the first and going to the last.

Now change the print statement to be controlled by a if statement that will only be true when element from the list is equal to a desired value that is given by the user. Use the equals method to do the compare.

import java.util.ArrayList;
import java.util.Scanner;
 
public class IndexOf {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        ArrayList<Integer> arrayList = new ArrayList<>();
        int input;
        while (true) {
            input = scanner.nextInt();
            if (input == -1) {
                break;
            }
            arrayList.add(input);
        }
        System.out.println("search for? ");
 
        for (int loopValue = 0; loopValue < arrayList.size(); loopValue++) {
            int input2 = scanner.nextInt();
            if (input == input2) {
                System.out.println(arrayList.get(loopValue));
 
            }
        }
 
    }
}

After searching for the value to input, it keeps printing the 2nd input value that I have entered 5 times according to the loop and its condition. I am still confused on how to approach this method and is there a possibility not to use any method such as hashmap, collections or the equals method? I am trying to find a mathematical or linear approach without using methods that automate or instantly give the answer or what I am looking for

Originally Posted by Norm

The code to read the user's input is inside of the loop. That means the user is required to enter a value every time the loop goes around. Is that what you want? I thought the user's input would be obtained one time before the search loop and then the loop would be used to compare each element in the list against the user's input.
Since the user's input is an int and the list contains Integer objects, there needs to be code to get the int value from the Integer object before using the == to compare their values.


The code is NOT comparing the element from the list against the user's input. I would expect input to have the -1 value that was detected to exit the first loop.
Use the get method to access an element in the list (See how the print statement does it) and then compare that value with what the user entered.

1. My bad, I only want the user to input a number that is within the array list once, I will put that outside the loop and before it.
2. from my understanding to the 'there needs to be a code to get the integer value from the integer elements(objects)' do you mean i need to assign a new integer variable to the array list and compare it with the new input which is input2? Because if I say input == input2 that includes the -1 indeed and it is out of the index and cannot be compared to the searchingValue input.

Originally Posted by Norm

Look at the API doc for the Integer class to see what method to call to get its int value. There is no need for a new variable.
Your code would look something like:

It is possible to chain calls to methods together when the preceding method (get) returns an object value (an Integer) then one of that object's methods (getIntValue) can be called on that object.
Look at the API doc for Integer to get the correct method name.

Now at this part I am kind of lost, please give me time to look for it and try to understand what you are saying.