Graph Bug Fix Walkthrough | Dataford Interview Questions

Debug a pre-written buggy solution to a graph problem similar to Number of Islands: find the logical flaws, fix them, and walk through the corrected solution, covering edge cases, readability and scalability.

Asked in the Round 3 (debugging, final) stage. Review the provided Python implementation and correct it without changing the function interface.

Input and Output

grid is a rectangular list of lists containing only strings "0" and "1". Return the number of four-directionally connected groups of "1" cells. Diagonal cells are not connected. The function may mark visited land cells in grid.

Constraints

0 <= len(grid) <= 300
If grid is non-empty, 1 <= len(grid[0]) <= 300
The grid is rectangular
Each cell is either "0" or "1"
Diagonal adjacency does not connect islands
The function may mutate grid to mark visited cells

Function Signature

def count_islands(grid):

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