Subset Leetcode, size of a List

November 15, 2021

I am really curios about one thing when compiling, in the given code below, where I am creating nested for loop, I am giving as a limit

subsetArr.size()

but when compiling it is saying memory exceeded, and if I define size just before the for loop

int size = subsetArr.size()

and then passing limit as size

i<size;

it is working fine. What can be the cause?

class Solution {
   public List<List<Integer>> subsets(int[] nums) {
    
    List<List<Integer>> subsetArr = new ArrayList<>();
    subsetArr.add(new ArrayList());
    
    for(int num: nums){ 
        for(int i=0; i<subsetArr.size(); i++){
            List<Integer> takenList = new ArrayList<>(subsetArr.get(i));
            takenList.add(num);
            subsetArr.add(takenList);
        }
    }
    
    return subsetArr;
}
}

>Solution :

Look at what this loop does:

for(int i=0; i<subsetArr.size(); i++){
    List<Integer> takenList = new ArrayList<>(subsetArr.get(i));
    takenList.add(num);
    subsetArr.add(takenList); // <-- here
}

Each iteration adds to the collection. So in the next iteration, subsetArr.size() will be larger. Thus you have a loop which indefinitely increases the size of the collection until it runs out of resources.

Contrast that to when you store the value:

int size = subsetArr.size();

In this case, while subsetArr.size() may change, size won’t unless you update it. So as long as you don’t update size then you have a finite loop.