<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 {
public:
    void dfs(vector<vector<int>>& grid,int i,int j,set<pair<int,int>>&s){
        if(i<0 || j<0 || i>=grid.size() || j>=grid[0].size() || s.find({i,j})!=s.end() || grid[i][j]==0)return;
        grid[i][j]=-1;
        s.insert({i,j});
        dfs(grid,i+1,j,s);
        dfs(grid,i,j+1,s);
        dfs(grid,i-1,j,s);
        dfs(grid,i,j-1,s);
    }
    int shortestBridge(vector<vector<int>>& grid) {
        int m=grid.size();
        int n=grid[0].size();
        set<pair<int,int>>s;
        bool flag=false;
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
            if(grid[i][j]==1){
                dfs(grid,i,j,s);
                flag=true;
            }
            if(flag==true)break;
        }
        if(flag==true)break;
    }
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
            cout<<grid[i][j]<<" ";
        }
        cout<<endl;
        }
        int ans=INT_MAX;
        queue<pair<int,int>>q;
        for(int i=0;i<m;i++)for(int j=0;j<n;j++)if(grid[i][j]==1)q.push({i,j});
        vector<int>d={0,1,0,-1,0};
        while(q.size()>0){
            int r=q.front().first;
            int c=q.front().second;
            q.pop();
            for(int i=0;i<4;i++){
                int nr=r+d[i];
                int nc=c+d[i+1];
                if(nr<0 || nc<0 || nr>=m || nc>=n )continue;
                if(grid[nr][nc]==-1){
                    ans=min(ans,grid[r][c]);
                    continue;
                }
                if(grid[nr][nc]!=0)continue;
                grid[nr][nc]=1+grid[r][c];
                q.push({nr,nc});
            }
        }
        return ans-1;
    }
};
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