<p>Given an <code>m x n</code> 2D binary grid <code>grid</code> which represents a map of <code>&#39;1&#39;</code>s (land) and <code>&#39;0&#39;</code>s (water), return <em>the number of islands</em>.</p>

<p>An <strong>island</strong> is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> grid = [
  [&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;]
]
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> grid = [
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;1&quot;]
]
<strong>Output:</strong> 3
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 300</code></li>
	<li><code>grid[i][j]</code> is <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
</ul>

WATER, LAND = "0", "1"

# class Grid:
#     def __init__(self, grid):
#         self._init_grid = grid
#         self
    
#     def _hash_grid():
#         result = {}
#         for row in range(len(grid)):
#             for col in range(len(grid[0])):
#                 result[(row, col)] = grid[row][col]
    
class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        if not grid:
            return 0
        result = 0
        visited = set()
        for row_index in range(len(grid)):
            for col_index in range(len(grid[0])):
                if grid[row_index][col_index] == WATER or (row_index, col_index) in visited:
                    continue
                island_points = self._island(row_index, col_index, grid)
                visited |= island_points
                result += 1

        return result

    def _island(self, row_index, col_index, grid):
        fringe = [(row_index, col_index)]
        result = set((row_index, col_index))
        while fringe:
            row, col = fringe.pop(0)
            # result.add((row, col))
            for neighbor in self._neighbors(row, col, grid):
                if neighbor not in result:
                    result.add(neighbor)
                    fringe.append(neighbor)
        return result

    def _neighbors(self, row, col, grid):
        result = []
        if row > 0 and grid[row-1][col] == LAND:
            result.append((row - 1, col))
        if row < len(grid) - 1 and grid[row+1][col] == LAND:
            result.append((row + 1, col))
        if col > 0 and grid[row][col-1] == LAND:
            result.append((row, col - 1))
        if col < len(grid[0]) - 1 and grid[row][col+1] == LAND:
            result.append((row, col + 1))
        return result

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