Generate All Permutations of Array in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start generating permutations by swapping elements.

DSA Python

def permute(nums, start=0):
    if start == len(nums) - 1:
        print(nums)
        return
    for i in range(start, len(nums)):
        nums[start], nums[i] = nums[i], nums[start]
        permute(nums, [1])
        nums[start], nums[i] = nums[i], nums[start]

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

Alen(nums)

Bi + 1

Cstart

Dstart + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i + 1' instead of 'start + 1' causes skipping elements.

Using 'start' again causes infinite recursion.

We move to the next index by increasing 'start' by 1 to generate permutations correctly.

2fill in blank

medium

Complete the code to print all permutations of the list.

DSA Python

def permute(nums, start=0):
    if start == len(nums) - 1:
        print([1])
        return
    for i in range(start, len(nums)):
        nums[start], nums[i] = nums[i], nums[start]
        permute(nums, start + 1)
        nums[start], nums[i] = nums[i], nums[start]

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

Astart

Blen(nums)

Cnums

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Printing 'start' or 'i' instead of the list.

Printing 'len(nums)' which is just the length.

We print the current permutation stored in 'nums' when we reach the last index.

3fill in blank

hard

Fix the error in the base case condition to correctly identify when to print a permutation.

DSA Python

def permute(nums, start=0):
    if start [1] len(nums):
        print(nums)
        return
    for i in range(start, len(nums)):
        nums[start], nums[i] = nums[i], nums[start]
        permute(nums, start + 1)
        nums[start], nums[i] = nums[i], nums[start]

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

A== len(nums) - 1

B< len(nums) - 1

C> len(nums)

D>= len(nums)

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>= len(nums)' causes index errors.

Using '< len(nums) - 1' never reaches base case.

The base case is when 'start' reaches the last index, which is length minus one.

4fill in blank

hard

Fill both blanks to create a function that returns all permutations as a list.

DSA Python

def permute(nums, start=0, result=None):
    if result is None:
        result = []
    if start == len(nums) - 1:
        result.append(nums[1])
        return
    for i in range(start, len(nums)):
        nums[start], nums[i] = nums[i], nums[start]
        permute(nums, start + 1, result)
        nums[start], nums[i] = nums[i], nums[start]
    return [2]

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

A[:]

Bcopy()

Cresult

Dnums

Attempts:

3 left

💡 Hint

Common Mistakes

Appending 'nums' directly causes all entries to be the same list.

Returning 'nums' instead of 'result' loses collected permutations.

We append a copy of 'nums' using slicing to avoid reference issues, and return 'result' list.

5fill in blank

hard

Fill all three blanks to generate permutations using backtracking and return the result list.

DSA Python

def permute(nums):
    result = []
    def backtrack(start=0):
        if start == [1]:
            result.append(nums[:])
            return
        for i in range(start, [2]):
            nums[start], nums[i] = nums[i], nums[start]
            backtrack(start + 1)
            nums[start], nums[i] = nums[i], nums[start]
    backtrack()
    return [3]

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

Alen(nums) - 1

Blen(nums)

Cresult

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'len(nums) - 1' as base case causes missing last permutation.

Returning 'nums' instead of 'result' loses all permutations.

The base case is when 'start' equals length of nums; loop runs to length; return collected 'result'.

Practice

1. What does the function permutations from Python's itertools module do when given an array as input?

easy

A. Generates all possible orderings of the elements in the array

B. Sorts the array in ascending order

C. Removes duplicate elements from the array

D. Returns the array reversed

Solution

1. Step 1: Understand the purpose of permutations

   The permutations function creates all possible ways to arrange the elements of the input array.

2. Step 2: Compare with other options

   Sorting, removing duplicates, or reversing are different operations and not what permutations does.

3. Final Answer:

   Generates all possible orderings of the elements in the array -> Option A

4. Quick Check:

   Permutations = all orderings [OK]

Hint: Permutations = all ways to arrange elements [OK]

Common Mistakes:

• Confusing permutations with sorting
• Thinking permutations remove duplicates
• Assuming permutations reverse the array

2. Which of the following is the correct syntax to generate all permutations of the list [1, 2, 3] using itertools.permutations in Python?

easy

A. from itertools import permutation
perms = permutations([1, 2, 3])

B. from itertools import permutation
perms = permutation([1, 2, 3])

C. import itertools
perms = itertools.permutations([1, 2, 3])

D. import itertools
perms = itertools.permutation([1, 2, 3])

Solution

1. Step 1: Check correct import and function name

   The correct module is itertools and the function is permutations (plural).

2. Step 2: Verify syntax correctness

   import itertools perms = itertools.permutations([1, 2, 3]) correctly imports itertools and calls itertools.permutations with the list.

3. Final Answer:

   import itertools perms = itertools.permutations([1, 2, 3]) -> Option C

4. Quick Check:

   Correct import and function name = import itertools perms = itertools.permutations([1, 2, 3]) [OK]

Hint: Use plural 'permutations' and correct import [OK]

Common Mistakes:

• Using singular 'permutation' instead of 'permutations'
• Wrong import statement
• Calling function without module prefix when not imported directly

3. What is the output of the following code?

from itertools import permutations
for p in permutations([1, 2]):
    print(p)

medium

A. (1, 2)\n(2, 1)

B. [1, 2]\n[2, 1]

C. (1, 2)\n(1, 2)

D. [1, 2]\n[1, 2]

Solution

1. Step 1: Understand permutations output type

   itertools.permutations returns tuples representing each permutation.

2. Step 2: List all permutations of [1, 2]

   They are (1, 2) and (2, 1), printed on separate lines.

3. Final Answer:

   (1, 2)\n(2, 1) -> Option A

4. Quick Check:

   Permutations of two elements = two tuples [OK]

Hint: Permutations output tuples, not lists [OK]

Common Mistakes:

• Expecting lists instead of tuples
• Repeating same permutation twice
• Confusing output format with string or list

4. The following code is intended to print all permutations of [1, 2, 3]. What is the error?

from itertools import permutations
perms = permutations([1, 2, 3])
print(perms)

medium

A. The import statement is incorrect

B. It prints a permutations object, not the permutations themselves

C. The list should be converted to a tuple first

D. The function permutations does not exist

Solution

1. Step 1: Understand what permutations returns

   permutations returns an iterator object, not a list of permutations directly.

2. Step 2: Printing the iterator shows its object info, not permutations

   To see permutations, you must iterate or convert to list first.

3. Final Answer:

   It prints a permutations object, not the permutations themselves -> Option B

4. Quick Check:

   Printing iterator shows object info, not data [OK]

Hint: Convert iterator to list to see permutations [OK]

Common Mistakes:

• Expecting print to show permutations directly
• Thinking import is wrong
• Believing input must be tuple

5. You want to generate all permutations of the array [1, 2, 2] but only keep unique permutations (no duplicates). Which approach correctly achieves this in Python?

hard

A. Use list(permutations([1, 2, 2])) directly

B. Use permutations(set([1, 2, 2])) to generate permutations of unique elements

C. Sort the array first, then use permutations

D. Use set(permutations([1, 2, 2])) to remove duplicate tuples

Solution

1. Step 1: Understand duplicates in permutations

   Input has repeated elements, so permutations include duplicates.

2. Step 2: Remove duplicates by converting permutations to a set

   Using set() on permutations removes duplicate tuples, keeping unique permutations only.

3. Final Answer:

   Use set(permutations([1, 2, 2])) to remove duplicate tuples -> Option D

4. Quick Check:

   Set removes duplicates from permutations [OK]

Hint: Convert permutations to set to remove duplicates [OK]

Common Mistakes:

• Using set on input list before permutations (loses duplicates)
• Assuming sorting removes duplicates
• Not removing duplicates at all