Number of Islands
Question
You're given a 2D grid representing a map that consists of '1's (land) and '0's (water). An island is a group of adjacent land that's surrounded by water vertically or horizontally.
Return the number of islands on the map.
Input: grid = [[1, 0 ], [0, 1]]
Output: 2
There are two separate islands in the corner of the grid.
Input: grid = [[1, 1, 1, 1, 0], [0, 1, 0, 0, 0], [1, 1, 0, 0, 0], [0, 0, 0, 0, 0]]
Output: 1
There is a single island in the top left corner of the grid.
Input: grid = [[1, 1, 1, 1, 1], [1, 0, 0, 0, 0], [1, 0, 1, 0, 0], [1, 0, 0, 0, 1], [1, 0, 1, 1, 1]]
Output: 3
There are three islands in this grid, one in the top-left edges, a second in the center, and a third in the bottom right corner of the grid.
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