CODEWITHSUNDEEP
javaalgorithmfor-looparraylist
user1810737
user1810737

Reputation: 234

Altering variables inside ArrayList with double for loop

I have an ArrayList called participatingUsers. Person has Person.money and Person.name that are interesting.

What I want to do is check the ArrayList against itself...

So I have this code

    for (Person debtHaver : this.participatingUsers) {

        // If they're in debt...
        if (debtHaver.getMoney() < 0) {

            // With someone...
            for (Person personToPay : this.participatingUsers) {

                // That's not themselves...
                if (!debtHaver.getName().equals(personToPay.getName())) {
                    // See if the personToPay is ranked higher than the
                    // debtHaver...
                    if (personToPay.getMoney() > 0) {

                        // If the debtee can pay the debter in full
                        if (-debtHaver.getMoney() <= personToPay.getMoney()) {
                            payment += debtHaver.getName() + " has to pay " + personToPay.getName() + " " + -debtHaver.getMoney() + "\n";
                            debtHaver.increaseMoney(-debtHaver.getMoney());
                            personToPay.decreaseMoney(-debtHaver.getMoney());
                        }

                        if (-debtHaver.getMoney() > personToPay.getMoney())
                        {
                            //But if he can't pay in full... Just pay the small bit you can pay.
                            payment += debtHaver.getName() + " has to pay " + personToPay.getName() + " " + personToPay.getMoney() + "\n";
                            debtHaver.increaseMoney(personToPay.getMoney());
                            personToPay.decreaseMoney(personToPay.getMoney());
                        }
                    }
                }
            }
        }
    }
    return payment;

Basically, I have a double for loop where I check each person against itself. If someone is in debt and has a negative amount of money, seek if there is someone who they can pay, then pay that person. The thing is, personToPay is not being updated in the arrayList debtHaver is in. I'm basically editing two different ArrayLists instead of the same one. What's the best way to deal with this issue?

Upvotes: 1

Views: 122

Answers (1)

Andrii Polunin
Andrii Polunin

Reputation: 1306

You are editing the same list. The problem is probably in this code:

debtHaver.increaseMoney(-debtHaver.getMoney());
personToPay.decreaseMoney(-debtHaver.getMoney());

You are putting debtHaver's amount to zero by the first line. And then you try to modify personToPay with zero amount. Just swap two lines of code and it should work:

personToPay.decreaseMoney(-debtHaver.getMoney());
debtHaver.increaseMoney(-debtHaver.getMoney());

Upvotes: 2

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