Number of Islands BFS and DFS in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start BFS from the given cell.

DSA Typescript

queue.push([row, [1]]);

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

Acol

Brow

Cgrid

Dvisited

Attempts:

3 left

💡 Hint

Common Mistakes

Pushing only the row index.

Pushing the grid or visited array instead of column.

We push the current cell's column index along with the row to the queue to start BFS.

2fill in blank

medium

Complete the code to mark the current cell as visited.

DSA Typescript

visited[[1]][col] = true;

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

Arow

Bcol

Cgrid

Dqueue

Attempts:

3 left

💡 Hint

Common Mistakes

Marking visited using column index only.

Marking grid or queue instead of visited.

We mark the current row and column as visited to avoid revisiting.

3fill in blank

hard

Fix the error in the DFS recursive call to explore neighbors.

DSA Typescript

dfs(grid, row + [1], col + [2], visited);

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A1

B0

C-1

Drow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 for both row and column changes (no movement).

Using row variable instead of numeric offsets.

To explore neighbors, we add or subtract 1 from row or column. Here, row is decreased by 1 and column stays the same.

4fill in blank

hard

Fill both blanks to check if the neighbor cell is valid and unvisited.

DSA Typescript

if (row + [1] >= 0 && row + [1] < grid.length && col + [2] >= 0 && col + [2] < grid[0].length && !visited[row + [1]][col + [2]] && grid[row + [1]][col + [2]] === '1') {

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Adr

Bdc

C-1

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using fixed numbers instead of direction variables.

Not checking boundaries properly.

We use dr and dc as row and column direction offsets to check neighbors.

5fill in blank

hard

Fill all three blanks to create a loop over all four directions for BFS.

DSA Typescript

const directions = [[[1], 0], [[2], 0], [0, [3]], [0, -[3]]];

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

A1

B-1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 instead of 1 for direction offsets.

Mixing up positive and negative signs.

Directions represent up (1,0), down (-1,0), right (0,1), left (0,-1) moves.