Moderate Graphs Question 119 of 224

How do you count islands in a 2D grid of land and water?

DSA interview set · Speak this in 60–90 seconds · Faridabad & Delhi NCR

Flex — one line

Grid — rows + cols

Scan cells

Why interviewers care about Graphs:

This is a process

question about Graphs.

Panels listen for order,

trade-offs, and what you would actually do on a DSA project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

Before you speak the answer, walk the interviewer through these steps:

1
Define it
Scan cells
2
on land, increment the
count and DFS/BFS to sink or mark the whole connected component.
3
Time is O(rows*cols) and
space is O(rows*cols) in the worst-case recursion or queue.
4
Union-Find on land cells
is the disjoint-set version of the same idea.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

Here's a short line you can speak, broken into clear beats:

Say this line

“Time is O(rows*cols) and space is O(rows*cols) in the worst-case recursion or qu”

Break into beats

TimeisOrowscolsand

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Scan cells on land, increment the count and DFS/BFS to sink or mark the whole connected component.