Number of Islands DFS/BFS | Dataford Interview Questions

Given a 2D grid representing land (1) and water (0), calculate the total number of islands using DFS or BFS.

Implement num_islands(grid), where adjacent land cells are connected horizontally or vertically, but not diagonally. Return the number of distinct islands. The function may modify the input grid while marking visited land cells.

Input and Output

grid is a rectangular list of lists containing only 0 and 1. Return an integer count.

Constraints

The grid may be empty.
For a non-empty grid, 1 <= rows, columns <= 300.
Each cell is either 0 or 1.
Cells connect only horizontally or vertically.

Function Signature

def num_islands(grid):

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