Question

There are two arraylists:

ArrayList<Integer[]> arr1 = new ArrayList<Integer[]>();
ArrayList<Integer[]> arr2 = new ArrayList<Integer[]>();
arr1.add(new Integer[]{1,2,3});
arr1.add(new Integer[]{1,2,2});
arr1.add(new Integer[]{1,2,3});
arr1.add(new Integer[]{1,1,1});
arr1.add(new Integer[]{1,1,1});

arr2.add(new Integer[]{1,2,3});
arr2.add(new Integer[]{1,2,2});

How to delete rows from arr1 that appear in arr2 and that are non-unique in arr1? E.g. in this example I would need to delete only {1,2,3}, because it appears more than once in arr1. The only solution that comes to my mind is to use 4 FOR loops, but it seems to be very inefficient solution.

Edit#1
Resulting arr1: {1,2,3},{1,2,2},{1,1,1},{1,1,1}

Answer 1

In case if you can use a List instead of array then you could do something as follows:

List<List<Integer>> arr1 = new ArrayList<List<Integer>>();        
List<List<Integer>> arr2 = new ArrayList<List<Integer>>();

arr1.add(Arrays.asList(new Integer[]{1, 2, 3}));
arr1.add(Arrays.asList(new Integer[]{1, 2, 3}));
arr1.add(Arrays.asList(new Integer[]{1, 2, 2}));
arr1.add(Arrays.asList(new Integer[]{1, 2, 3}));
arr1.add(Arrays.asList(new Integer[]{1, 1, 1}));
arr1.add(Arrays.asList(new Integer[]{1, 1, 1}));

arr2.add(Arrays.asList(new Integer[]{1, 2, 3}));
arr2.add(Arrays.asList(new Integer[]{1, 2, 2}));

System.out.println(arr1);
System.out.println(arr2);

Set<List<Integer>> set1 = new HashSet<List<Integer>>();        
Iterator<List<Integer>> it = arr1.iterator(); 

while(it.hasNext()) {
    List<Integer> curr = it.next();
    if(!set1.add(curr) && arr2.contains(curr)) {
        it.remove();
    }
}

System.out.println(arr1);

Output:

[[1, 2, 3], [1, 2, 3], [1, 2, 2], [1, 2, 3], [1, 1, 1], [1, 1, 1]]
[[1, 2, 3], [1, 2, 2]]
[[1, 2, 3], [1, 2, 2], [1, 1, 1], [1, 1, 1]]