Double Ended Queue Deque in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the front index of the deque to -1.

DSA C

int front = [1];

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A-1

B0

C1

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing front to 0 causes confusion with valid index.

In deque implementation, front is initialized to -1 to indicate the deque is empty.

2fill in blank

medium

Complete the code to check if the deque is full when using a circular array of size MAX.

DSA C

if ((front == 0 && rear == MAX - 1) || (front == rear + 1)) {
    // Deque is full
    [1];
}

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Aexit(1)

Breturn 0

Cprintf("Full")

Dreturn 1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 0 instead of 1 for full condition.

Return 1 to indicate the deque is full in the isFull function.

3fill in blank

hard

Fix the error in the code that inserts an element at the front of the deque.

DSA C

void insertFront(int deque[], int *front, int *rear, int value) {
    if (isFull(*front, *rear)) {
        printf("Deque is full\n");
        return;
    }
    if (*front == -1) {
        *front = 0;
        *rear = 0;
    } else if (*front == 0) {
        *front = [1];
    } else {
        (*front)--;
    }
    deque[*front] = value;
}

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A1

B0

CMAX - 1

D*front - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting front to 0 causes overwrite of first element.

When front is at 0, moving it to MAX - 1 wraps around the circular array.

4fill in blank

hard

Fill both blanks to correctly delete an element from the rear of the deque.

DSA C

void deleteRear(int deque[], int *front, int *rear) {
    if (*front == -1) {
        printf("Deque is empty\n");
        return;
    }
    if (*front == *rear) {
        *front = [1];
        *rear = [2];
    } else if (*rear == 0) {
        *rear = MAX - 1;
    } else {
        (*rear)--;
    }
}

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A-1

B0

C1

DMAX - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting front or rear to 0 instead of -1 after last deletion.

When the last element is deleted, both front and rear are reset to -1 to indicate empty deque.

5fill in blank

hard

Fill all three blanks to correctly insert an element at the rear of the deque.

DSA C

void insertRear(int deque[], int *front, int *rear, int value) {
    if (isFull(*front, *rear)) {
        printf("Deque is full\n");
        return;
    }
    if (*front == -1) {
        *front = [1];
        *rear = [2];
    } else if (*rear == MAX - 1) {
        *rear = [3];
    } else {
        (*rear)++;
    }
    deque[*rear] = value;
}

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

A0

B-1

DMAX - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Incorrectly initializing front or rear to -1 when inserting first element.

When deque is empty, front and rear start at 0. If rear reaches MAX - 1, it wraps to 0.