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Thread: Help in ArrayList of ArrayLists

  1. #1
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    Question Help in ArrayList of ArrayLists

    Here is my code to return all the possible subsets of a set.

    Now my question is why when we uncomment the 1. line then the code works fine

    But when we uncomment the 2. line it simply returns a empty set

    why?

    Please help me with the logic behind it.

    ********************************************Code** ***********************************************
    public class Solution {
    public ArrayList<ArrayList<Integer>> ans;

    public void calc(ArrayList<Integer> A,ArrayList<Integer> arr,int top){
    for(int i = top;i<A.size();i++){
    arr.add(A.get(i));
    ArrayList<Integer> temp = new ArrayList<>();
    for(int j = 0;j<arr.size();j++){
    temp.add(arr.get(j));
    }
    if(!ans.contains(temp)){
    ans.add(temp);
    }
    calc(A,arr,i+1);
    arr.remove(arr.size()-1);
    }
    }

    public ArrayList<ArrayList<Integer>> subsetsWithDup(ArrayList<Integer> A) {
    Collections.sort(A);
    ans = new ArrayList<>();
    ArrayList<Integer> temp = new ArrayList<>();
    // 1. ans.add(new ArrayList<>());
    // 2. ans.add(temp);
    calc(A,temp,0);
    return ans;


    }
    }

    ***************************************code******* *******************************************

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Help in ArrayList of ArrayLists

    Please post the main method so the code can be compiled and executed for testing.

    The variable: ans should not be a class level variable. If methods require access to it, it should be passed to the method as an argument.

    Please edit your post and wrap your code with code tags:

    [code]
    **YOUR CODE GOES HERE**
    [/code]

    to get highlighting and preserve formatting.
    If you don't understand my answer, don't ignore it, ask a question.

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