[LintCode/LeetCode] Subsets & Subsets II

Subsets

Problem

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

Notice

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

Example

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

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

Challenge

Can you do it in both recursively and iteratively?

Solution

class Solution {
    public ArrayList<ArrayList<Integer>> subsets(int[] nums) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        if (nums == null || nums.length == 0) return res;
        ArrayList<Integer> cur = new ArrayList<>();
        Arrays.sort(nums);
        dfs(nums, cur, res, 0);
        return res;
    }
    public void dfs(int[] nums, ArrayList<Integer> cur, ArrayList<ArrayList<Integer>> res, int index) {
        if (index > nums.length) return;
        res.add(new ArrayList<Integer> (cur));
        for (int i = index; i < nums.length; i++) {
            cur.add(nums[i]);
            dfs(nums, cur, res, i+1);
            cur.remove(cur.size()-1);
        }
    }
}

Subsets II

Problem

Given a list of numbers that may has duplicate numbers, return all possible subsets

##Notice

Each element in a subset must be in non-descending order.
The ordering between two subsets is free.
The solution set must not contain duplicate subsets.
Have you met this question in a real interview? Yes

Example

If S = [1,2,2], a solution is:

[
  [2],
  [1],
  [1,2,2],
  [2,2],
  [1,2],
  []
]

Challenge

Can you do it in both recursively and iteratively?

Solution

class Solution {
    public ArrayList<ArrayList<Integer>> subsetsWithDup(ArrayList<Integer> S) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        Collections.sort(S);
        ArrayList<Integer> cur = new ArrayList<>();
        dfs(S, cur, res, 0);
        return res;
    }
    public void dfs(ArrayList<Integer> S, ArrayList<Integer> cur, ArrayList<ArrayList<Integer>> res, int index) {
        if (index > S.size()) return;
        res.add(new ArrayList<Integer> (cur));
        for (int i = index; i < S.size(); i++) {
            if (i != index && S.get(i) == S.get(i-1)) continue;
            cur.add(S.get(i));
            dfs(S, cur, res, i+1);
            cur.remove(cur.size()-1);
        }
    }
}