全组合

import java.util.ArrayList;
import java.util.List;

public class Solution {

    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        result.add(new ArrayList<>());

        for (int num : nums) {
            List<List<Integer>> tmp = new ArrayList<>();
            for (List<Integer> res : result) {
                List<Integer> list = new ArrayList<>(res);
                list.add(num);
                tmp.add(list);
            }
            result.addAll(tmp);
        }
        return result;
    }

    public static void main(String[] args) {
        int[] nums = {1, 2, 3};
        List<List<Integer>> result = new Solution().subsets(nums);
        System.out.println(result);
    }
}

[参考]https://discuss.leetcode.com/topic/9031/simple-java-solution-with-for-each-loops