<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 {
    int dx[4] = {0,1,0,-1};
    int dy[4] = {1,0,-1,0};
    void dfs(int i,int j,int n,int m, vector<vector<int>>&grid,vector<vector<bool>>&vis){
        if(i>=0 && i<n && j>=0 && j<m && vis[i][j] == false && grid[i][j]==1){
            vis[i][j] = true;
            for(int dir=0;dir<4;dir++){
                int ni = i + dx[dir];
                int nj = j + dy[dir];
                dfs(ni,nj,n,m,grid,vis);
            }
        }
    }
public:
    int shortestBridge(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();
        vector<vector<bool>>vis(n,vector<bool>(m,false));
        bool f = true;
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j] == 1){
                    dfs(i,j,n,m,grid,vis);
                    f = false;
                    break;
                }
            }
            if(!f) break;
        }
        queue<pair<int,int>>q;
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(vis[i][j]){
                    q.push({i,j});
                }
            }
        }
        int dis = 0;
        while(!q.empty()){
            int x = q.size();
            while(x--)
            {
                auto [x,y] = q.front();
                q.pop();
                for(int dir=0;dir<4;dir++){
                    int nx = x + dx[dir];
                    int ny = y + dy[dir];
                    if(nx>=0 && nx<n && ny>=0 && ny<m && vis[nx][ny]==false){
                        if(grid[nx][ny] == 1) return dis;
                        vis[nx][ny] = true;
                        q.push({nx,ny});
                    }
                }
            }
            cout<<endl<<endl;
            dis++;
        }
        return dis;
    }
};
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