Advanced · 2D lists · 181 of 264
Count the islands
A map shows land (#) and water (.). Land squares touching up, down, left or right belong to the same island. Count the islands.
Input: r and c, then r lines of c characters. Output: the number of islands.
Examples
Input
4 5 ##... ##..# ...## #....
Output
3
Input
1 1 .
Output
0
Input
3 3 #.# .#. #.#
Output
5
One more test checks other inputs when you press Check.
Stuck? The idea behind 2d lists
A list of lists is a grid: grid[row][col]. Read one row per line, each turned into numbers.
Loop over rows, then over the columns inside each row. zip(*grid) turns rows into columns.
grid = [[1, 2, 3], [4, 5, 6]]
for row in grid:
print(*row)
print(grid[1][2]) # 6Watch for: [[0] * 3] * 2 makes two names for the same row: changing one changes both. Build rows with a comprehension: [[0] * 3 for _ in range(2)].