<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 {
    void visit(vector<vector<int>>& grid,int i,int j,unordered_map<int,unordered_map<int,bool>>&vis,queue<pair<int,int>>&vp){
        if(i<0 || j<0 || i>=grid.size() || j>=grid.size() || vis[i][j] || grid[i][j]==0) return;
        vis[i][j]=true;
        vp.push({i,j});
        visit(grid,i,j+1,vis,vp);
        visit(grid,i,j-1,vis,vp);
        visit(grid,i-1,j,vis,vp);
        visit(grid,i+1,j,vis,vp);
    }
public:
    int shortestBridge(vector<vector<int>>& grid) {
        queue<pair<int,int>>vp;
        unordered_map<int,unordered_map<int,bool>>vis;
        int n=grid.size();
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j]==1){
                    visit(grid,i,j,vis,vp);
                    goto label;
                }
            }
        }
        label:
        cout<<n*n<<endl;
        // cout<<vp.size()<<endl;
        vp.push({-1,-1});
        int ans=0;
        while(!vp.empty()){
            // cout<<vp.size()<<" ";
            // if(vp.size()>8100){
            //     cout<<vp.size()<<" ";
            //     cout<<vp.front().first<<" ";
            // }
            auto top=vp.front();
            vp.pop();
            if(top.first==-1){
                if(!vp.empty()){
                    vp.push({-1,-1});
                }
                ans++;
                // cout<<ans<<endl;
                continue;
            }

            int i=top.first,j=top.second;

           
            if(i-1>=0 && !vis[i-1][j]){
                if(grid[i-1][j]==1) return ans;
                vp.push({i-1,j});
                 vis[i-1][j]=true;
            }
            if(i+1<n && !vis[i+1][j]){
                 if(grid[i+1][j]==1) return ans;
                vp.push({i+1,j});
                 vis[i+1][j]=true;
            }
            if(j+1<n && !vis[i][j+1]){
                 if(grid[i][j+1]==1) return ans;
                vp.push({i,j+1});
                 vis[i][j+1]=true;
            }
            if(j-1>=0 && !vis[i][j-1]){
                 if(grid[i][j-1]==1) return ans;
                vp.push({i,j-1});
                 vis[i][j-1]=true;
            }
            
        }
        return 0;
    }
};
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