Leetcode 题目解析之 Subsets

Given a set of distinct integers, nums, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,

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

[

3,

1,

2,

1,2,3,

1,3,

2,3,

1,2,

[]

]

    int target;// 次数
    Integer[] stack;// 存储每次排列
    List<List<Integer>> rt;// 存储结果
    public void search(int p, int[] nums) {
        // 若长度为k，则stack是其中一个结果，保存结果
        if (p == target) {
            rt.add(new ArrayList<Integer>(Arrays.asList(stack)));
            return;
        }
        for (int i = 0; i < nums.length; i++) {
            if (p > 0 && nums[i] <= stack[p - 1]) {
                continue;
            }
            stack[p] = nums[i];
            search(p + 1, nums);
        }
    }
    public List<List<Integer>> subsets(int[] nums) {
        Arrays.sort(nums);
        rt = new ArrayList<List<Integer>>();
        // 分别做0~num.length长度的组合
        for (int i = 0; i <= nums.length; i++) {
            target = i;
            stack = new Integer[i];
            search(0, nums);
        }
        return rt;
    }