Is Subsets II easy or hard?

Subsets II is generally considered a medium-level problem. Generating subsets alone is straightforward, but correctly handling duplicate elements adds complexity. Understanding sorting and pruning duplicate branches in backtracking is the key challenge.

How to solve Subsets II in O(n)?

Generating all subsets cannot be done in O(n) time because the output itself can contain up to 2^n subsets. Any correct algorithm must at least enumerate those subsets. The optimal practical complexity is O(n·2^n) using backtracking or iterative subset construction.

What is the best approach for Subsets II?

Backtracking with sorting is the most common solution. Sorting groups duplicate numbers together, and the recursion skips repeated values at the same depth using a simple condition. This prevents generating duplicate subsets while still exploring all valid combinations. The complexity is O(n·2^n) time with O(n) recursion stack space.

What data structure is used in Subsets II?

The main data structures are arrays or lists to store the current subset and the final result list. The algorithm also relies on sorting the array first to group duplicates. Recursion stacks or iterative lists are used to expand subsets step by step.

What is the time complexity of Subsets II?

The time complexity is O(n·2^n). A set with n elements has up to 2^n subsets, and copying each subset into the result may take O(n) time. Both the backtracking and iterative approaches have the same asymptotic complexity.

Subsets II Python or Java solution approach?

Both Python and Java implementations typically use the same backtracking strategy. Sort the array, recursively build subsets, and skip duplicates with a condition that checks if the current value equals the previous value at the same recursion level. This produces only unique subsets efficiently.

Is Subsets II asked at Google, Amazon, or Meta?

Subsets-style problems frequently appear in interviews at companies like Amazon, Google, and Meta. Variants include Subsets, Subsets II, Combination Sum, and Permutations with duplicates. Interviewers use these problems to evaluate recursion, pruning strategies, and handling duplicates.

90. Subsets II - Practice Online

Given an integer array nums that may contain duplicates, return all possible subsets (the power set).

The solution set must not contain duplicate subsets. Return the solution in any order.

Example 1:

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

Example 2:

Input: nums = [0]
Output: [[],[0]]

Constraints:

1 <= nums.length <= 10
-10 <= nums[i] <= 10