遍历包含ArrayList的ArrayList

Question

I am working on a bagging problem. I am given a list of items(ints), and bags that have a maxSize. I am trying to find the least possible amount of bags to fit all the items. I need to do this in a recursive method.

I am storing bag objects (That are ArrayList of integers, with some helper methods of checking if the size + an int will be greater than the maxSize of the bag). I am then storing all of these bags in an ArrayList objects. The problem I am running into is I seem to be adding every item to every bag. Below is the method I believe the problem is. I can't think of a way to exit once I have found I can add the item to the bag at 'i'. At this point I need to get a new item, and try to bag it at the first bag, if it doesn't fit then try the second, third etc.

baggedList = ArrayList :::: recList = List of ints I am trying to bag

I feel like I am over complicating this. If you have any better suggestions please do tell.

    public boolean bagging (ArrayList<Integer> recList){

    boolean keepBagging = true;
    System.out.println("right before the recursive method");
    System.out.println("the reclist before while loop" + recList.toString());

    while (!recList.isEmpty() && keepBagging){
        int item = recList.remove(recList.size() -1);
        for (int i= 0; i < baggedList.size(); i ++){
            System.out.println("i = " + i + " Item = " + item);
            if (tryToBag(item, i)){ //boolean method
                addItem (item, i); //adds the item
                bagging (recList); //recursive call
            }
            else {
                System.out.println("FAILED" + keepBagging);
                keepBagging = false;
            }
        }
    }
    return keepBagging;
}

CanBag method that calls a Bag method

    private boolean tryToBag(int item, int i) {

    boolean canBag = false;
    Bag currentBag = baggedList.get(i);
    ArrayList<Integer> list = currentBag.getList();

    if (currentBag.canBag(item)){
        canBag = true;
    }
    return canBag;
}

canBag method

    public boolean canBag(int size){

    if (size + Bag.sum() <= maxBagSize){
        return true;
    }
    else return false;
}

toString

    public String toString(){
    int counter = 0;
    String ret = "";
    for (int i = 0; i < baggedList.size(); i++){
        Bag tryThisBag = baggedList.get(i);
        ret += "bag " + counter + tryThisBag.getList().toString();
        counter++;
    }
    return ret;
}

addItem method

    private void addItem(int item, int i) {
    Bag currentBag = baggedList.remove(i); //removing list
    ArrayList<Integer> list = currentBag.getList(); // new list
    list.add(item); //adding item
    System.out.println ("List here at bag" + i + " : " + list.toString());
    currentBag.setList(list); // sets the arrayList back to the bag object
    baggedList.add(i, currentBag); //sets the bag at the index in the collection of bags

}

Answer 1

public boolean bagging (ArrayList<Integer> recList){

boolean keepBagging = true;
System.out.println("right before the recursive method");
System.out.println("the reclist before while loop" + recList.toString());

while (!recList.isEmpty() && keepBagging) {
    int item = recList.remove(recList.size() -1);
    for (int i= 0; i < baggedList.size(); i ++){
        System.out.println("i = " + i + " Item = " + item);
        if (tryToBag(item, i)){ //boolean method
            addItem (item, i); //adds the item
            break;
        }
        else {
            System.out.println("FAILED" + keepBagging);
            keepBagging = false;
        }
    }
}
return keepBagging;
}

I merely just added a break call into your code, it's hard to understand what you are going for. You shouldn't need to recurse with this. If you can try to bag and you add an item, then break and then remove the next item and loop over some more. Is this what you wanted? Or on success, should it continue to the next iteration?

Answer 2

For each item in reclist, try to find a slot in bags, if found break out of for loop and move to the next item in the reclist

while (!recList.isEmpty()) {
int item = recList.remove(recList.size() -1);
for (int i= 0; i < baggedList.size(); i ++){
    System.out.println("i = " + i + " Item = " + item);
    if (tryToBag(item, i)){ //boolean method
        addItem (item, i); //adds the item
    }
  break;
  }
}

Answer 3

我取消了此版本，并以不同的方式开始了新版本。