Given a 2D grid where "1" represents land and "0" represents water, count the number of distinct islands. An island is a group of adjacent land cells connected horizontally or vertically (not diagonally).
For example:
1 1 0 0 0 1 1 0 0 0 0 0 1 0 0 0 0 0 1 1 -> 3 islands
Explain your approach, including how you track visited cells.
How to approach it
- Hint 1
Iterate through every cell. When you find a '1', that's a new island -- then mark all connected land.
- Hint 2
DFS or BFS from each unvisited land cell will visit the entire island.
- Hint 3
You can mark cells as visited by changing '1' to '0' in-place, or use a separate visited set.
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