1. Description

Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: The solution set must not contain duplicate subsets.

2. Example

If nums = [1,2,3], a solution is:
[
[3],
[1],
[2],
[1,2,3],
[1,3],
[2,3],
[1,2],
[]
]

3. Code

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

public class LeetCode0078 {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        if (nums == null || nums.length == 0) {
            return result;
        }
        dfs(0, nums, new ArrayList<Integer>(), result);
        result.add(new ArrayList<Integer>());
        return result;
    }

    private void dfs(int index, int[] nums, List<Integer> current, List<List<Integer>> result) {

        if (index >= nums.length) {
            return;
        }

        current.add(nums[index]);
        result.add(new ArrayList<>(current));
        dfs(index + 1, nums, current, result);
        current.remove(current.size() - 1);
        dfs(index + 1, nums, current, result);
    }

    public static void main(String[] args) {
        LeetCode0078 leetcode = new LeetCode0078();
        List<List<Integer>> result = leetcode.subsets(new int[] { 1, 2, 3 });
        for (int i = 0; i < result.size(); i++) {
            for (int j = 0; j < result.get(i).size(); j++) {
                System.out.print(result.get(i).get(j) + " ");
            }
            System.out.println();
        }
    }
}