Using remove and add method for list

Question

Move the first half of cards into firstHalf // This may or may not be done in one line of code Move the remaining elements in cards into secondHalf // This may or may not be done in one line of code While there are elements in firstHalf Remove the element at the start of firstHalf and add it to cards Remove the element at the start of secondHalf and add it to cards EndWhile If secondHalf has any elements remaining Remove the element at the start of secondHalf and add it to cards EndIf

this is the error I am getting. Why is my list growing if I am removing?Should I be doing something like this inside my first for loop firstHalf.add(cards.remove(0));
cards= firstHalf.add(cards.remove(0));

this is the error I am getting
shuffle() should not change the number of elements in cards. cards had contained a complete 52 card deck, but now has size: 71 expected:<52> but was:<71>

public void shuffle(ListGenerator gen) {


    List<PlayingCard> firstHalf = gen.createNewList();
    List<PlayingCard> secondHalf = gen.createNewList();
    for (int i = 0; i <= (cards.size() / 2); i++) {
     firstHalf.add(cards.remove(0));
    }
    secondHalf.addAll(cards);
    while (firstHalf.isEmpty() == false) {
        cards.add(firstHalf.remove(0));
        cards.add(secondHalf.remove(0));
    }
    if (secondHalf.isEmpty() == false) {
        cards.add(secondHalf.remove(0));
    }
}*

Whats ListGenerator ?

SamHoque
– SamHoque

2018-10-17 01:21:42 +00:00
Commented Oct 17, 2018 at 1:21 — SamHoque
– SamHoque, Commented Oct 17, 2018 at 1:21

Pavneet_Singh · Accepted Answer · 2018-10-17 01:22:03Z

3

you need to clear the cards because cards still has elements which were previously added to secondHalf

secondHalf.addAll(cards);
cards.clear();
//^^^^^^^^^^^^

answered Oct 17, 2018 at 1:22

Pavneet_Singh

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5 Comments

Clyde Over a year ago

this is the error I am getting now shuffle() should not change the number of elements in cards. cards had contained a complete 52 card deck, but now has size: 37 expected:<52> but was:<37>. should I be doing something like for (int i = (cards.size() / 2) ; i <= cards.size() ; i++) { secondHalf.add(cards.remove(0)); }

Pavneet_Singh Over a year ago

can you explain the error? (although you can use Collections.shuffle(cards);)

Pavneet_Singh Over a year ago

try int l = cards.size() / 2; for(int i = 0; i <= l ; i++) , avoid calculating the size at runtime in loop during every iteration

Clyde Over a year ago

Is the firstHalf of the list cards (cards.size()/2) or is it (cards.size()-1/2)?

Pavneet_Singh Over a year ago

both are same 51/2 will give you 25 and as you are cards.remove(0) so you get first half in firstHalf

shmosel · Accepted Answer · 2018-10-17 01:22:05Z

1

When you call secondHalf.addAll(cards);, you're not removing those cards from cards. Add this afterwards:

cards.clear();

answered Oct 17, 2018 at 1:22

shmosel

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2 Comments

Clyde Over a year ago

for someone reason this is still changing the size of my list

Clyde Over a year ago

this is the error i get shuffle() should not change the number of elements in cards. cards had contained 4 complete card decks for a total of 208 cards, but now has size: 141 expected:<208> but was:<141>

suraz · Accepted Answer · 2018-10-17 03:02:36Z

1

You are using the same variable i.e card in for loop and also removing the item from same card variable. Therefore, you are actually adding less number of element in firstHalf and your card still has the size that exceeds half of its original size.

 for (int i = 0; i <= (cards.size() / 2); i++) {
  firstHalf.add(cards.remove(0));
}

the size of firstHalf after the for loop ::18

the size of the card after the for loop::34

you should use the different variable for loop. like:

List<Integer> cardSize = cards.size();
  for (int i = 0; i <= (cardSize / 2); i++) {
  firstHalf.add(cards.remove(0));
}

I believe it should solve your issue.

answered Oct 17, 2018 at 3:02

suraz

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Comments

Fred O'Rourke · Accepted Answer · 2018-10-17 01:22:17Z

0

I'd expect

secondHalf.addAll(cards);

Doesn't remove the entries from cards. Add a test after that line to see if cards is empty.

answered Oct 17, 2018 at 1:22

Fred O'Rourke

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Comments

dilshani shashinika · Accepted Answer · 2018-10-17 01:42:29Z

0

secondHalf.addAll(cards)

Here you are adding elements to the secondHalf, but you didn't remove the elements in cards. Add below line to code.

cards.clear();

answered Oct 17, 2018 at 1:42

dilshani shashinika

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