<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(int x,int y,vector<vector<int>> &grid,vector<vector<bool>> &visit,vector<int> delx, vector<int> dely,map<pair<int,int>,set<pair<int,int>>> &mpp,pair<int,int> parent)
    {
        visit[x][y]=true;
        mpp[parent].insert({x,y});
        for (int i=0;i<4;i++)
        {
            int nr=x+delx[i];
            int nc=y+dely[i];
            if (nr>=0 && nr<grid.size() && nc>=0 && nc<grid.size() && !visit[nr][nc] && grid[nr][nc]==1)
            {
                dfs(nr,nc,grid,visit,delx,dely,mpp,parent);
            }
        }
    }
    int shortestBridge(vector<vector<int>>& grid) {
        int n=grid.size();
        vector<int> delx={-1,0,+1,0};
        vector<int> dely={0,-1,0,+1};
        map<pair<int,int>,set<pair<int,int>>> mpp;
        vector<vector<bool>> visit(n,vector<bool>(n,false));
        vector<pair<int,int>> store;
        for (int i=0;i<n;i++)
        {
            for (int j=0;j<n;j++)
            {
                if (!visit[i][j] && grid[i][j]==1)
                {
                    pair<int,int> parent={i,j};
                    store.push_back({i,j});
                    visit[i][j]=true;
                    mpp[{i,j}].insert({i,j});
                    dfs(i,j,grid,visit,delx,dely,mpp,parent);
                }
                    
            }
        }
        pair<int,int> firstIsland=store[0];
        pair<int,int> secondIsland=store[1];
        int ans=INT_MAX;
        /*
        cout<<"First\n";
        for (auto it: mpp[firstIsland])
        {
            cout<<it.first<<" "<<it.second<<endl;
        }
        cout<<"Second\n";
        for (auto it: mpp[secondIsland])
        {
            cout<<it.first<<" "<<it.second<<endl;
        }
        */
        for (auto it: mpp[firstIsland])
        {
            for (auto it1: mpp[secondIsland])
            {
                pair<int,int> coA=(it);
                pair<int,int> coB=(it1);
                int x;
                x=abs(coA.first - coB.first) + abs(coA.second - coB.second);
                ans=min(ans,x-1);
            }
        }
        return ans;                
    }
};
37285