Dutch National Flag Three Way Partition in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the low pointer at the start of the array.

DSA Python

def dutch_flag_partition(arr, pivot):
    low = [1]
    mid = 0
    high = len(arr) - 1
    while mid <= high:
        pass

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

Apivot

Blen(arr)

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting low at len(arr) causes index errors.

Using pivot as index is incorrect.

The low pointer starts at index 0 to begin partitioning from the start.

2fill in blank

medium

Complete the code to swap elements when the mid element is less than the pivot.

DSA Python

def dutch_flag_partition(arr, pivot):
    low = 0
    mid = 0
    high = len(arr) - 1
    while mid <= high:
        if arr[mid] < pivot:
            arr[low], arr[[1]] = arr[[1]], arr[low]
            low += 1
            mid += 1

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

Alow

Bmid

Chigh

Dpivot

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping with high pointer causes wrong partition.

Swapping with low pointer twice is incorrect.

We swap arr[low] and arr[mid] when arr[mid] is less than pivot, then move both pointers forward.

3fill in blank

hard

Fix the error in the code to correctly handle the case when arr[mid] is greater than the pivot.

DSA Python

def dutch_flag_partition(arr, pivot):
    low = 0
    mid = 0
    high = len(arr) - 1
    while mid <= high:
        if arr[mid] > pivot:
            arr[mid], arr[[1]] = arr[[1]], arr[mid]
            high -= 1

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

Ahigh

Blow

Cpivot

Dmid

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping with low pointer causes wrong partition.

Moving mid pointer after swap here is incorrect.

When arr[mid] is greater than pivot, swap arr[mid] with arr[high] and decrease high pointer.

4fill in blank

hard

Fill both blanks to complete the while loop that partitions the array correctly.

DSA Python

def dutch_flag_partition(arr, pivot):
    low = 0
    mid = 0
    high = len(arr) - 1
    while [1] <= [2]:
        if arr[mid] < pivot:
            arr[low], arr[mid] = arr[mid], arr[low]
            low += 1
            mid += 1
        elif arr[mid] > pivot:
            arr[mid], arr[high] = arr[high], arr[mid]
            high -= 1
        else:
            mid += 1

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

Amid

Blow

Chigh

Dpivot

Attempts:

3 left

💡 Hint

Common Mistakes

Using low in loop condition causes infinite loops.

Using pivot in condition is incorrect.

The loop continues while mid is less than or equal to high to process all elements.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that counts elements less than, equal to, and greater than the pivot.

DSA Python

def count_partition(arr, pivot):
    return { [1]: sum(1 for x in arr if x [2] pivot) for [3] in ['less', 'equal', 'greater'] }

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

A'less', 'equal', 'greater'

B==

Cx

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using pivot as variable name causes errors.

Using '<' for all conditions is incorrect.

The comprehension iterates over keys and counts elements matching the condition x == pivot for 'equal'.