Java - Adding multiple user inputs into arraylist

Question

I am attempting to read an infinite amount of numbers input on the same line from user (separated by a space) and print the square of all values above 0 - all without using for loops.

For example...

Input:

1 2 3 4 -10 -15

Output:

30

Below is the code I have so far:

ArrayList<Integer> numbers = new ArrayList<Integer>();

    //insert into array if > 0
    int x = sc.nextInt();
    if(x > 0){
        numbers.add(x);
    }

    //square numbers array
    for (int i = 0; i < numbers.size(); ++i) {
        numbers.set(i, numbers.get(i) * numbers.get(i));
    }

    //sum array
    int sum = 0;
    for(int i = 0; i < numbers.size(); ++i){
        sum += numbers.get(i);
    }
    System.out.println(sum);

As you can see I am just scanning one input from the user as i'm not sure how to tackle storing infinite input. Furthermore, I am using for loops for my two equations.

Thanks

You can use split and then calculate.

Shubhendu Pramanik
– Shubhendu Pramanik

2017-11-23 17:40:21 +00:00
Commented Nov 23, 2017 at 17:40 — Shubhendu Pramanik
– Shubhendu Pramanik, Commented Nov 23, 2017 at 17:40

MichalH · Accepted Answer · 2017-11-23 17:19:59Z

2

Since you're adding the square of each number, you don't really need any list, just a single number to which you add the square for each number you read from the input. Something like:

int result = 0;    
Scanner scanner = new Scanner(System.in);

while(scanner.hasNextInt()){
    int num = scanner.nextInt();
    if(num > 0)
        result += num * num;
}

System.out.println(result);

edited Nov 23, 2017 at 17:19

MichalH

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answered Nov 23, 2017 at 17:16

Kraylog

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1 Comment

0xgareth Over a year ago

Hi, thanks for the reply.. two things... When I run this and print/store the output e.g I/P: 5 5 5 & O/P: 25 50 75... how could I print/store the sum of the squares i.e 75 as shown above? Also, if I input: 1 -1 nothing happens

MichalH · Accepted Answer · 2017-11-23 17:53:16Z

1

As said in the first answer, you don't need an ArrayList.

But if you insisted on doing it that way, here is a solution:

To store the numbers, use this code:

while(sc.hasNextInt()){
    int x = sc.nextInt();
    if(x > 0){
        numbers.add(x);
    }
}

And the for loops can be avoided this way:

Instead of:

for (int i = 0; i < numbers.size(); ++i) {
    numbers.set(i, numbers.get(i) * numbers.get(i));
}

You can use:

List<Integer> newNumbers = numbers.stream().map(x->x*x).collect(toList());

answered Nov 23, 2017 at 17:53

MichalH

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2 Comments

0xgareth Over a year ago

Hi, this produces an error 'lambda expression cannot re declare another variable' and 'the method toList() is undefined for the test type

MichalH Over a year ago

@Gareth Hi, the first error is caused by the x in the lambda, you should rename it to something else, for example num->num*num. For the toList error use import static java.util.stream.Collectors.toList;.

Oghli · Accepted Answer · 2017-11-23 17:35:59Z

0

You can refactor your program using array list in this way:

ArrayList<Integer> numbers = new ArrayList<Integer>(); 
Scanner in = new Scanner(System.in);
while(in.hasNextInt()){
   int x = in.nextInt();
    if(x > 0){
        numbers.add(x * x);
    }
}
int sum = 0;
for(int i = 0; i < numbers.size(); i++){
    sum += numbers.get(i);
}
    System.out.println(sum);

answered Nov 23, 2017 at 17:35

Oghli

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Comments

Shubhendu Pramanik · Accepted Answer · 2017-11-23 17:36:49Z

0

You can use split after reading the line and then perform your calculation:

        int result = 0;
        Scanner scanner = new Scanner(System.in);

        String a[] = scanner.nextLine().split(" ");

        for (String aa : a) {
            if (Integer.parseInt(aa) > 0) {
                result = result + Integer.parseInt(aa) * Integer.parseInt(aa);
            }
        }
System.out.println(result);

I/P: 2 3 1 -44 -22

O/P 14

answered Nov 23, 2017 at 17:36

Shubhendu Pramanik

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Comments

Mustapha Belmokhtar · Accepted Answer · 2017-11-23 18:00:14Z

0

Using lambdas :

    ArrayList<Integer> numbers = new ArrayList<>();

    while (sc.hasNextInt()) {
        int x = sc.nextInt();
        if (x > 0) {
            numbers.add(x);
        }
    }

    int sum = numbers.stream().map(i -> i * i).reduce((xx, yy) -> xx + yy).get();
    System.out.println(sum);

answered Nov 23, 2017 at 18:00

Mustapha Belmokhtar

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