78. Subsets

/**
 * 78. Subsets
 * https://leetcode.com/problems/subsets/description/
 *
 * Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: The solution set must not contain duplicate subsets.

Example:

Input: nums = [1,2,3]
Output:
[
[3],
[1],
[2],
[1,2,3],
[1,3],
[2,3],
[1,2],
[]
]
 * */

class Solution {
    fun subsets(A: IntArray): List<List<Int>> {
        A.sort();
        val result = ArrayList<ArrayList<Int>>();
        helper(result, ArrayList<Int>(), A, 0);
        return result;
    }

    fun helper(result: ArrayList<ArrayList<Int>>, arr: ArrayList<Int>, A: IntArray, index: Int){
        result.add(ArrayList<Int>(arr));//new reference for arr
        for (i in index..(A.size - 1)) {
            arr.add(A[i]);
            helper(result, arr, A, i + 1);
            arr.removeAt(arr.size - 1);
        }
    }
}