Generate All Subsets Powerset in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start generating subsets by calling the helper function.

DSA Go

func subsets(nums []int) [][]int {
    result := [][]int{}
    helper(nums, 0, []int{}, &result)
    return [1]
}

Drag options to blanks, or click blank then click option'

Ahelper

Bresult

Cnums

D[]int{}

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the input slice instead of the result.

Returning the helper function call instead of the result.

The function returns the collected subsets stored in 'result'.

2fill in blank

medium

Complete the code to add the current subset copy to the result.

DSA Go

func helper(nums []int, index int, current []int, result *[][]int) {
    if index == len(nums) {
        temp := make([]int, len(current))
        copy(temp, current)
        *result = append(*result, [1])
        return
    }
    // recursive calls omitted for brevity
}

Drag options to blanks, or click blank then click option'

Atemp

Bcurrent

Cnums

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Appending 'current' directly causing all subsets to be the same.

Appending the original 'nums' slice.

We append a copy 'temp' of the current subset to avoid mutation issues.

3fill in blank

hard

Fix the error in the recursive call to include the next element in the subset.

DSA Go

func helper(nums []int, index int, current []int, result *[][]int) {
    if index == len(nums) {
        // base case
        return
    }
    // exclude current element
    helper(nums, index+1, current, result)
    // include current element
    helper(nums, index+1, [1], result)
}

Drag options to blanks, or click blank then click option'

Aappend(result, nums[index])

Bappend(nums, index)

Cappend(current, nums[index])

Dcurrent

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'current' without adding the element.

Appending to 'nums' or 'result' incorrectly.

We create a new slice by appending the current element to 'current' for the include case.

4fill in blank

hard

Fill both blanks to correctly start the helper function and append the current subset copy.

DSA Go

func subsets(nums []int) [][]int {
    result := [][]int{}
    [1](nums, 0, []int{}, &result)
    return result
}

func helper(nums []int, index int, current []int, result *[][]int) {
    if index == len(nums) {
        temp := make([]int, len(current))
        copy(temp, current)
        *result = append(*result, [2])
        return
    }
    helper(nums, index+1, current, result)
    helper(nums, index+1, append(current, nums[index]), result)
}

Drag options to blanks, or click blank then click option'

Ahelper

Bsubsets

Ccurrent

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the wrong function name.

Appending the original 'current' slice instead of the copy.

Call 'helper' to start recursion and append the copied slice 'temp' to result.

5fill in blank

hard

Fill all three blanks to complete the helper function with base case, exclude, and include logic.

DSA Go

func helper(nums []int, index int, current []int, result *[][]int) {
    if [1] == len(nums) {
        temp := make([]int, len(current))
        copy(temp, current)
        *result = append(*result, temp)
        return
    }
    helper(nums, index+1, current, result) // exclude
    helper(nums, index+1, [2], result) // include
}

func subsets(nums []int) [][]int {
    result := [][]int{}
    [3](nums, 0, []int{}, &result)
    return result
}

Drag options to blanks, or click blank then click option'

Aindex

Bappend(current, nums[index])

Chelper

Dnums

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable in base case.

Not appending element correctly.

Calling wrong function name.

Check if 'index' reached end, include element by appending, and call 'helper' to start recursion.

Practice

1. What does the term powerset mean in the context of sets?

easy

A. The set of elements repeated twice

B. All possible subsets of a given set including empty and full set

C. The set itself without any subsets

D. Only the subsets with exactly two elements

Solution

1. Step 1: Understand the definition of powerset

   The powerset of a set is the collection of all possible subsets, including the empty set and the set itself.

2. Step 2: Compare options with definition

   All possible subsets of a given set including empty and full set correctly describes the powerset as all subsets. Other options describe partial or incorrect concepts.

3. Final Answer:

   All possible subsets of a given set including empty and full set -> Option B

4. Quick Check:

   powerset = all subsets [OK]

Hint: Powerset means every subset possible [OK]

Common Mistakes:

• Thinking powerset excludes empty set
• Confusing powerset with subsets of fixed size
• Assuming powerset duplicates elements

2. Which of the following Go code snippets correctly initializes an empty slice of slices of integers to store subsets?

easy

A. var subsets [][]int = []int{}

B. var subsets []int = []int{}

C. var subsets []int = [][]int{}

D. var subsets [][]int = [][]int{}

Solution

1. Step 1: Identify the type for storing subsets

   Subsets are slices of integers, so a slice of slices of int is needed: [][]int.

2. Step 2: Check initialization syntax

   var subsets [][]int = [][]int{} correctly initializes an empty slice of slices of int. Other options mismatch types.

3. Final Answer:

   var subsets [][]int = [][]int{} -> Option D

4. Quick Check:

   Correct slice of slices initialization [OK]

Hint: Use [][]int for slice of int slices [OK]

Common Mistakes:

• Using []int instead of [][]int for subsets
• Mixing types in initialization
• Incorrect empty slice syntax

3. What is the output of the following Go code that generates all subsets of []int{1, 2}?

func subsets(nums []int) [][]int {
    res := [][]int{{}}
    for _, num := range nums {
        newSubsets := [][]int{}
        for _, subset := range res {
            newSubset := append([]int{}, subset...)
            newSubset = append(newSubset, num)
            newSubsets = append(newSubsets, newSubset)
        }
        res = append(res, newSubsets...)
    }
    return res
}

func main() {
    result := subsets([]int{1, 2})
    fmt.Println(result)
}

medium

A. [[], [1, 2]]

B. [[1], [2], [1, 2]]

C. [[], [1], [2], [1, 2]]

D. [[], [2], [1]]

Solution

1. Step 1: Trace initial state and first iteration

   Start with res = [[]]. For num=1, add subsets [1], so res = [[], [1]].

2. Step 2: Trace second iteration

   For num=2, add subsets [2] and [1,2], so res = [[], [1], [2], [1, 2]].

3. Final Answer:

   [[], [1], [2], [1, 2]] -> Option C

4. Quick Check:

   All subsets of {1,2} listed [OK]

Hint: Start with empty subset, add each number to existing subsets [OK]

Common Mistakes:

• Missing empty subset in result
• Not appending new subsets correctly
• Confusing order of subsets

4. The following Go code attempts to generate all subsets of []int{1, 2}. What is the bug?

func subsets(nums []int) [][]int {
    res := [][]int{{}}
    for _, num := range nums {
        for i := range res {
            res[i] = append(res[i], num)
            res = append(res, [][]int{res[i]})
        }
    }
    return res
}

medium

A. Appending to res[i] modifies original subsets causing duplicates

B. res is not initialized properly

C. Loop variable num is not used

D. Function returns nil instead of subsets

Solution

1. Step 1: Understand slice append behavior in loop

   Appending to res[i] modifies the original slice in res because slices share underlying arrays.

2. Step 2: Identify consequence of modifying original subsets

   This causes all subsets to be changed and duplicates appear, breaking correct subset generation.

3. Final Answer:

   Appending to res[i] modifies original subsets causing duplicates -> Option A

4. Quick Check:

   Modify copy, not original slice [OK]

Hint: Copy slice before append to avoid modifying original [OK]

Common Mistakes:

• Appending directly to loop variable slice
• Not creating new slice copy
• Ignoring slice reference behavior

5. Given a set []int{1, 2, 2} with duplicate elements, which approach correctly generates all unique subsets (powerset without duplicates)?

hard

A. Sort input, then use backtracking skipping duplicates when choosing elements

B. Use a map to store subsets as keys without sorting input

C. Generate all subsets and then remove duplicates by comparing slices

D. Ignore duplicates and generate subsets normally

Solution

1. Step 1: Understand duplicate handling in subsets

   Duplicates cause repeated subsets if not handled carefully.

2. Step 2: Use sorting and skip duplicates during backtracking

   Sorting input helps detect duplicates. Skipping duplicates when choosing elements avoids repeated subsets efficiently.

3. Final Answer:

   Sort input, then use backtracking skipping duplicates when choosing elements -> Option A

4. Quick Check:

   Sort + skip duplicates = unique subsets [OK]

Hint: Sort input and skip duplicates during recursion [OK]

Common Mistakes:

• Not sorting input before backtracking
• Removing duplicates after generation (inefficient)
• Ignoring duplicates causing repeated subsets