Split a list into two sublists in all possible ways

Question

I have a list of variable size, for example

[1, 2, 3, 4]

and I want to get every possible way to split this list into two:

Answer 1

Though in Python, it's quite easy to get the result with its extensive library, in Java, you can write a recursive solution. The following will print all possible combinations of your array:

public static void main(String[] args) {
    List num = Arrays.asList(1, 2, 3, 4);
    List> sublists = new ArrayList>();
    for (int i = 0; i <= num.size(); i++) {
      permutation(num, sublists, i, new ArrayList(), 0);
    }

    for (List subList : sublists) {
        List numCopy = new ArrayList(num);
        numCopy.removeAll(subList);
        System.out.println("(" + subList + ", " + numCopy + ")");
    }
}

public static void permutation(List nums, List> subLists, int sublistSize, List currentSubList,
      int startIndex) {
    if (sublistSize == 0) {
      subLists.add(currentSubList);
    } else {
      sublistSize--;
      for (int i = startIndex; i < nums.size(); i++) {
        List newSubList = new ArrayList(currentSubList);
        newSubList.add(nums.get(i));
        permutation(nums, subLists, sublistSize, newSubList, i + 1);
      }
    }
}

The sublists carries all the combinations found till now. The last parameter is the startIndex for the next element of current sublist. That is to avoid duplicates.