how do I access the first and last row of an arraylist of arraylist

Question

I was wondering how I could access the first and last row of this 2d arraylist.

public static ArrayList<Integer> list(ArrayList<ArrayList<Integer>> grid){

    ArrayList<Integer> num = new ArrayList<>();

    for(int i = 0; i < grid.size(); i++){
        for( int j = 0; j <grid.get(i).size(); j++){
            System.out.print(grid.get(i).get(j) + " ");
        }
        System.out.println();
    }

this code will print out the entire arraylist. Is there a way to get the first row and last row only

3 4 1 2 8 6

6 1 8 2 7 4

5 4 3 9 9 5

5 9 8 3 2 6

8 7 2 9 6 4

What values do i and j have while the first row is being printed? What values do they have while the last row is being printed? You can either add more print calls, or use the debugger to answer that question. — tgdavies
– tgdavies, Commented Mar 20, 2022 at 6:17
sorry for the confusion, I mean to either print the first row only [3 4 1 2 8 6], or print the last row[8 7 2 9 6 4]. — still_learning
– still_learning, Commented Mar 20, 2022 at 6:21
I just figure out how to print the first row. Any thoughts on how to print just the last row? — still_learning
– still_learning, Commented Mar 20, 2022 at 6:27
You already know how to get the number of rows. And you know that the final index is one less than that. — shmosel
– shmosel, Commented Mar 20, 2022 at 6:31

Jhanzaib Humayun · Accepted Answer · 2022-03-20 06:45:31Z

1

grid.get(0) gives you the first row, and grid.get(grid.size()-1) gives you the last row.

If you want to print them out then do this:

public static ArrayList<Integer> list(ArrayList<ArrayList<Integer>> grid){
ArrayList<Integer> num = new ArrayList<>();

int[] firstLastIndices = new int[]{0, grid.size()-1}
for(int i : firstLastIndices){
    for( int j = 0; j <grid.get(i).size(); j++){
        System.out.print(grid.get(i).get(j) + " ");
    }
    System.out.println();
}

edited Mar 20, 2022 at 6:45

answered Mar 20, 2022 at 6:40

Jhanzaib Humayun

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