<p>You are given an <code>n x n</code> binary matrix <code>grid</code> where <code>1</code> represents land and <code>0</code> represents water.</p>

<p>An <strong>island</strong> is a 4-directionally connected group of <code>1</code>&#39;s not connected to any other <code>1</code>&#39;s. There are <strong>exactly two islands</strong> in <code>grid</code>.</p>

<p>You may change <code>0</code>&#39;s to <code>1</code>&#39;s to connect the two islands to form <strong>one island</strong>.</p>

<p>Return <em>the smallest number of </em><code>0</code><em>&#39;s you must flip to connect the two islands</em>.</p>

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

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

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

<pre>
<strong>Input:</strong> grid = [[0,1,0],[0,0,0],[0,0,1]]
<strong>Output:</strong> 2
</pre>

<p><strong class="example">Example 3:</strong></p>

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

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

<ul>
	<li><code>n == grid.length == grid[i].length</code></li>
	<li><code>2 &lt;= n &lt;= 100</code></li>
	<li><code>grid[i][j]</code> is either <code>0</code> or <code>1</code>.</li>
	<li>There are exactly two islands in <code>grid</code>.</li>
</ul>

class Solution:
    def shortestBridge(self, grid: List[List[int]]) -> int:
        n = len(grid)
        direction = [(1,0),(-1,0),(0,1),(0,-1)]
        island = set()
        def island_mark(i,j):
            island.add((i,j))
            for x,y in direction:
                if 0<=i+x<=n-1 and 0<=j+y<=n-1 and grid[i+x][j+y] and (i+x,j+y) not in island:
                    island_mark(i+x,j+y)
                    island.add((i+x,j+y))
        flag=False
        for i in range(n):
            for j in range(n):
                if grid[i][j] == 1: 
                    island_mark(i,j)
                    flag=True
                    break
            if flag:break
                
        print(island)
        queue = list(island)
        shortest_bridge = 0
        while queue:
            new_queue = []
            while queue:
                i,j = queue.pop()
                for x,y in direction:
                    if 0<=i+x<=n-1 and 0<=j+y<=n-1 and (i+x,j+y) not in island:
                        if grid[i+x][j+y] == 1: return shortest_bridge
                        new_queue.append((i+x,j+y))
                        island.add((i+x,j+y))
            queue = new_queue
            shortest_bridge += 1
            print(queue,shortest_bridge)
        return shortest_bridge
20500