Quick Sort Partition Lomuto and Hoare in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the pivot element in Lomuto partition.

DSA C++

int lomutoPartition(int arr[], int low, int high) {
    int pivot = arr[[1]];
    int i = low - 1;
    for (int j = low; j < high; j++) {
        if (arr[j] <= pivot) {
            i++;
            std::swap(arr[i], arr[j]);
        }
    }
    std::swap(arr[i + 1], arr[high]);
    return i + 1;
}

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

Ahigh

Bhigh - 1

Clow + 1

Dlow

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing the pivot as the first element instead of the last.

Using an index outside the array bounds.

In Lomuto partition, the pivot is chosen as the last element, which is at index 'high'.

2fill in blank

medium

Complete the code to initialize the pointer for Hoare partition.

DSA C++

int hoarePartition(int arr[], int low, int high) {
    int pivot = arr[low];
    int i = [1];
    int j = high + 1;
    while (true) {
        do {
            i++;
        } while (arr[i] < pivot);
        do {
            j--;
        } while (arr[j] > pivot);
        if (i >= j) return j;
        std::swap(arr[i], arr[j]);
    }
}

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

Alow - 1

Bhigh

Chigh - 1

Dlow

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing 'i' at low instead of low - 1.

Confusing the start positions of 'i' and 'j'.

In Hoare partition, 'i' starts just before the low index, so it is initialized to low - 1.

3fill in blank

hard

Fix the error in the Lomuto partition swap condition.

DSA C++

int lomutoPartition(int arr[], int low, int high) {
    int pivot = arr[high];
    int i = low - 1;
    for (int j = low; j < high; j++) {
        if (arr[j] [1] pivot) {
            i++;
            std::swap(arr[i], arr[j]);
        }
    }
    std::swap(arr[i + 1], arr[high]);
    return i + 1;
}

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

A>

B>=

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<=' causing wrong partitioning.

Using '==' which only moves elements equal to pivot.

The condition arr[j] <= pivot ensures elements less than or equal to pivot are moved left.

4fill in blank

hard

Fill both blanks to complete the Hoare partition loop conditions.

DSA C++

int hoarePartition(int arr[], int low, int high) {
    int pivot = arr[low];
    int i = low - 1;
    int j = high + 1;
    while (true) {
        do {
            i++;
        } while (arr[i] [1] pivot);
        do {
            j--;
        } while (arr[j] [2] pivot);
        if (i >= j) return j;
        std::swap(arr[i], arr[j]);
    }
}

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

A<=

B>=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators causing infinite loops.

Mixing up the directions of 'i' and 'j' pointers.

In Hoare partition, 'i' moves forward while arr[i] < pivot, and 'j' moves backward while arr[j] > pivot.

5fill in blank

hard

Fill all three blanks to complete the Lomuto partition swap and return.

DSA C++

int lomutoPartition(int arr[], int low, int high) {
    int pivot = arr[high];
    int i = low - 1;
    for (int j = low; j < high; j++) {
        if (arr[j] <= pivot) {
            i[1];
            std::swap(arr[i], arr[j]);
        }
    }
    std::swap(arr[i [2] 1], arr[[3]]);
    return i + 1;
}

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

A++

B+

Chigh

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i+' instead of 'i++' causing syntax errors.

Swapping with wrong indices causing incorrect partition.

We increment 'i' with '++', swap arr[i + 1] with arr[high], and return i + 1 as the pivot index.