Leetcode Combination Sum Problem. Problem understanding the 15th line

Question

Hi I am new to Data Structure and I have some problem understanding the line "ds.remove(ds.size()-1);". Could anyone please help me out here?

class Solution {

private void findCombinations(int ind,int[] arr,int target,List<List<Integer>> ans, List<Integer> ds)
{
    if(ind == arr.length)
    {
        if(target == 0)
            ans.add(new ArrayList<>(ds));
        return;
    }
    if(arr[ind] <= target)
    {
        ds.add(arr[ind]);
        findCombinations(ind, arr, target - arr[ind], ans, ds);
        ds.remove(ds.size() - 1);
    }
    findCombinations(ind + 1, arr, target, ans, ds);
}

public List<List<Integer>> combinationSum(int[] candidates, int target) {
    List<List<Integer>> ans = new ArrayList<>();
    findCombinations(0, candidates, target, ans, new ArrayList<>());
    return ans;
}

}

Answer 1

With this line you are deleting the last element inside the array. ds.size() is the number of elements inside the array, for example there are 2 elements, if you want to get the index of the last element you have to say ds.size() - 1 since the first elements has an index of 0 and the second one index of 1