Shortest Path in Unweighted Graph Using BFS in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the queue for BFS.

DSA C

int queue[MAX];
int front = -1, rear = -1;

// Enqueue function
void enqueue(int x) {
    rear = rear [1] 1;
    queue[rear] = x;
    if (front == -1) front = 0;
}

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

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' causes rear to move backward.

Using '*' or '/' is incorrect for pointer movement.

We increase rear by 1 to add a new element at the end of the queue.

2fill in blank

medium

Complete the code to mark a node as visited in BFS.

DSA C

int visited[MAX] = {0};

void bfs(int start) {
    visited[start] = [1];
    enqueue(start);
    // rest of BFS
}

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

A1

B0

C-1

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Marking visited as 0 means unvisited.

Using node value instead of 1 is incorrect.

Marking visited[start] as 1 means the node is visited.

3fill in blank

hard

Fix the error in the BFS loop condition to process all nodes in the queue.

DSA C

while (front [1] -1 && front <= rear) {
    int current = queue[front];
    front = front + 1;
    // process current
}

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

A!=

B==

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' causes loop to run only when front is -1.

Using '<' or '>' is incorrect for this condition.

The loop should run while front is not -1 and front <= rear.

4fill in blank

hard

Fill both blanks to update distance and enqueue neighbors in BFS.

DSA C

if (!visited[neighbor]) {
    visited[neighbor] = 1;
    distance[neighbor] = distance[current] [1] 1;
    enqueue([2]);
}

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

A+

B-

Cneighbor

Dcurrent

Attempts:

3 left

💡 Hint

Common Mistakes

Subtracting 1 from distance is wrong.

Enqueueing current instead of neighbor causes infinite loop.

Distance to neighbor is current distance plus 1; enqueue the neighbor node.

5fill in blank

hard

Fill all three blanks to print the shortest path distance after BFS.

DSA C

int shortest_path(int start, int end) {
    bfs(start);
    if (distance[end] == [1]) {
        return -1; // no path
    } else {
        return distance[[2]];
    }
}

// Usage
int dist = shortest_path(0, [3]);

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

A-1

Bend

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking distance == 0 instead of -1.

Returning distance of start node instead of end.

Using wrong end node in function call.

If distance[end] is -1, no path exists; return distance[end]; example end node is 5.