How to store this pattern in Java arraylist?

Question

I want to store the below array pattern in List, I am not understanding how to implement this as it has alternate increment.

Increment the number by 399.
Increment by 1

and continue the above 2 steps for a certain length of numbers. If someone can guide me for the logic with simple OOPs concepts

0, 400, 401, 800, 801, 1200, 1201, 1600, 1601, 2000

What have you tried? Seems like you just need to alternate the increment each time through the loop. — Dave Newton
– Dave Newton, Commented Jul 11, 2020 at 15:45
I have written to implement by 399 but how to alternate is what I can't think of — Pankaj Kumar
– Pankaj Kumar, Commented Jul 11, 2020 at 15:49
Shouldn't your list be 0, 399, 400, 799, 800...? Otherwise you're incrementing by 400, then 1. — NomadMaker
– NomadMaker, Commented Jul 11, 2020 at 15:51
Seems like you're new to programming, and if true, I guess everyone will agree that you should give it a though yourself and not ask for it on Stack Overflow. In the end if at all you don't find a solution yourself, you can google about alternating series and see how it's done. — Debargha Roy
– Debargha Roy, Commented Jul 11, 2020 at 15:51
How would you alternate IRL? You’d probably remember what you alternated by the previous iteration, and switch to the other one based on what you did last time. — Dave Newton
– Dave Newton, Commented Jul 11, 2020 at 15:54

sabraship · Accepted Answer · 2020-07-11 16:05:56Z

1

You could also do something like this:

//add the first item outside of the loop, so that you can access the previous item within it
list.add(1)

//loop through the list in increments of 2
for (int i = 1; i < length; i += 2) {
   list.add(list.get(i - 1) + 399);
   list.add(list.get(i) + 1);
}

answered Jul 11, 2020 at 16:05

sabraship

991 silver badge9 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Pankaj Kumar · Accepted Answer · 2020-07-11 16:19:06Z

0

Figured it out, this is what I wrote now, and it workds

int pages = 8;

    List<Integer> numArray = new ArrayList<Integer>();
    
    numArray.add(0);

    boolean incrementFlag = false;
    int i = 400;
    for (int j = 0; j < (pages-1); j++) {

        numArray.add(i);
        if (incrementFlag)
            i += 399;
        else
            i += 1;

        incrementFlag = !incrementFlag;

    }

edited Jul 11, 2020 at 16:19

answered Jul 11, 2020 at 16:00

Pankaj Kumar

411 silver badge14 bronze badges

2 Comments

akuzminykh Over a year ago

Why do you add to i?

Dave Newton Over a year ago

Glad you worked out a solution. The flag is redundant; you could just use the increment value as the flag since you can check its value, but that’s an implementation detail. You could also use a ternary op to select the value to add, but that’s another minor implementation detail. Good work.

Collectives™ on Stack Overflow

How to store this pattern in Java arraylist?

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related