LeetCode 200 - Number of Islands - 2022.12.24 solution

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        # How to solve it: iterate through the cells.  If you find a land
        # cell, increment the number of found islands by 1 and then
        # run DFS to find its extent and add those positions to set of
        # already-discovered land.
        ROWS = len(grid)
        COLS = len(grid[0])
        found_land_positions = set()
        number_of_discovered_islands = 0
        found_water_positions = set()
        def find_adjacent_land_positions(y, x):
            neighbors = [
                [0, 1],
                [0, -1],
                [1, 0],
                [-1, 0],
            ]
            adjacent_positions = [(y + n[0], x + n[1]) for n in neighbors]
            for pos in adjacent_positions:
                if pos[0] < 0 or pos[0] > ROWS - 1 or \
                   pos[1] < 0 or pos[1] > COLS - 1:
                   continue
                if (pos[0], pos[1]) in found_land_positions or (pos[0], pos[1]) in found_water_positions:
                    continue
                if grid[pos[0]][pos[1]] == "0":
                    found_water_positions.add((i, j))
                if grid[pos[0]][pos[1]] == "1":
                    found_land_positions.add((pos[0], pos[1]))
                    find_adjacent_land_positions(pos[0], pos[1])

        i = 0
        while i < len(grid):
            j = 0
            while j < len(grid[0]):
                if grid[i][j] == "0":
                    found_water_positions.add((i, j))
                if (i, j) in found_land_positions:
                    pass
                elif grid[i][j] == "1":
                    number_of_discovered_islands += 1
                    found_land_positions.add((i, j))
                    find_adjacent_land_positions(i, j)
                j += 1
            i += 1
        return number_of_discovered_islands