从ArrayList移除一个int <Integer> 使用索引但被视为对象java

Question

I am trying to remove an int from an ArrayList containing [9, 0, 0, 6, 2, 3, 0, 0, 0] using the following code

static void appendRow(ArrayList<ArrayList<Integer>> ans) {
    int ind = 0;

    while(yolo.size() < 81) {
        for(int x = 0; x < ans.size(); x++) {
            ArrayList<Integer> an = ans.get(x);
            for(int i = ind; i < ind+3; i++) {
                yolo.add(an.get(i));
            }
            for(int y = 0; y < 3; y++) {
                an.remove(y);
            }
        }
        ind+=3;
    }
    System.out.println(yolo);
}

What happened here is that after I add the first 3 ints from ans, I will delete them. There are more than one items that will be passed into the appendRow function but I only need the first three and the next function only needs the rest (ie [6, 2, 3, 0, 0, 0]).

The problem is that when y = 2, an.remove(y) does not remove the 0 with index of 2, instead it removes 2 so the list becomes [0, 6, 3, 0, 0, 0], which is totally wrong.

Answer 1

Reverse the direction of your for loop. Change

for (int y = 0; y < 3; y++) {
    an.remove(y);
}

to something like

for (int y = 2; y >= 0; y--) {
    an.remove(y);
}

or something like

for (int y = 0; y < 3; y++) {
    an.remove(0);
}

because when your remove the first element the second element is now what was the third. That is 9, 0, 0, 6, 2, 3, 0, 0, 0 becomes 0, 0, 6, 2, 3, 0, 0, 0 then 0, 6, 2, 3, 0, 0, 0 and then your reported 0, 6, 3, 0, 0, 0 (which is exactly what you told it to do).