<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>

class Solution:
    def __init__(self):
        self.__directions = [[1, 0], [-1, 0], [0, 1], [0, -1]]

    def numIslands(self, grid: List[List[str]]) -> int:
        # edge case
        if not grid:
            return 0
        
        visited = set()
        islandCount = 0
        for row in range(len(grid)):
            for col in range(len(grid[row])):
                if grid[row][col] == "1" and (row, col) not in visited:
                    self.__exploreIsland(grid, row, col, visited)
                    islandCount += 1
        
        return islandCount
    
    def __exploreIsland(self, grid: List[List[str]], row: int, col: int, visited: Set[Tuple[int, int]]) -> None:
        # base case
        if grid[row][col] != "1":
            return
        elif (row, col) in visited:
            return 

        visited.add((row, col)) 
        for rowOffset, colOffset in self.__directions:
            newRow = row + rowOffset
            newCol = col + colOffset
            if (0 <= newRow < len(grid) and 0 <= newCol < len(grid[row])):
                self.__exploreIsland(grid, newRow, newCol, visited)


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