78. Subsets (Medium)

https://leetcode.com/problems/subsets/

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

Note: The solution set must not contain duplicate subsets.

Example:

Input: nums = [1,2,3]
Output:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

Solutions

1.

class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> ans = new ArrayList<>();

        List<Integer> track = new ArrayList<>();

        combine(0, nums, track, ans);

        return ans;
    }

    private void combine(int depth, int[] nums, List<Integer> track, List<List<Integer>> ans) {
        if (depth == nums.length) {
            List<Integer> sol = new ArrayList<>(track);

            ans.add(sol);

            return;
        }

        track.add(nums[depth]);
        combine(depth + 1, nums, track, ans);
        track.remove(track.size()-1);

        combine(depth + 1, nums, track, ans);
    }
}

2.

class Solution2 {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> ans = new ArrayList<>();
        ans.add(new ArrayList<>());

        int len = nums.length;
        for (int i = 0; i < len; i++) {
            int ansSize = ans.size();

            for (int j = 0; j < ansSize; j++) {
                List<Integer> sol = new ArrayList<>(ans.get(j));

                ans.add(sol);

                sol.add(nums[i]);
            }
        }

        return ans;
    }
}

Incorrect Solutions

References

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