求一个集合的所有子集,网上的方法没有注释看不懂,请看得动代码的高手帮忙注释一下!谢过!
public class Solution {
public ArrayList> subsets(int[] num) {
ArrayList> result = new ArrayList>();
if(num == null || num.length == 0) {
return result;
}
ArrayList list = new ArrayList();
Arrays.sort(num);
subsetsHelper(result, list, num, 0);
return result;
}
private void subsetsHelper(ArrayList<ArrayList<Integer>> result,
ArrayList<Integer> list, int[] num, int pos) {
result.add(new ArrayList<Integer>(list));
for (int i = pos; i < num.length; i++) {
list.add(num[i]);
subsetsHelper(result, list, num, i + 1);
list.remove(list.size() - 1);
}
}
}