<p>Given an <code>n x n</code> binary matrix <code>grid</code>, return <em>the length of the shortest <strong>clear path</strong> in the matrix</em>. If there is no clear path, return <code>-1</code>.</p>

<p>A <strong>clear path</strong> in a binary matrix is a path from the <strong>top-left</strong> cell (i.e., <code>(0, 0)</code>) to the <strong>bottom-right</strong> cell (i.e., <code>(n - 1, n - 1)</code>) such that:</p>

<ul>
	<li>All the visited cells of the path are <code>0</code>.</li>
	<li>All the adjacent cells of the path are <strong>8-directionally</strong> connected (i.e., they are different and they share an edge or a corner).</li>
</ul>

<p>The <strong>length of a clear path</strong> is the number of visited cells of this path.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/18/example1_1.png" style="width: 500px; height: 234px;" />
<pre>
<strong>Input:</strong> grid = [[0,1],[1,0]]
<strong>Output:</strong> 2
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/18/example2_1.png" style="height: 216px; width: 500px;" />
<pre>
<strong>Input:</strong> grid = [[0,0,0],[1,1,0],[1,1,0]]
<strong>Output:</strong> 4
</pre>

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

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

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

<ul>
	<li><code>n == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 &lt;= n &lt;= 100</code></li>
	<li><code>grid[i][j] is 0 or 1</code></li>
</ul>

class Solution {
    int n;
    vector<vector<bool>> visited;
    queue<pair<int,int>> q;
    vector<vector<int>> grid;
    bool inBox(int i,int j){
        return i>-1 && i<n && j>-1 && j<n;
    }
    
    vector<pair<int,int>> adj(int i,int j){
        // cout<<"change\n";
        cout<<i<<" "<<j<<endl;
        vector<pair<int,int>> ans;
        for(int di = -1;di<=1;di++){
            for(int dj = -1;dj<=1;dj++){
                // cout<<di<<" "<<dj<<endl;
                if(di == 0 && dj == 0) continue;
                int resi = i+di;
                int resj = j+dj;

                if(!inBox(resi,resj)) continue ;
                if(grid[resi][resj] != 0) continue;
                
                ans.push_back({resi,resj});
            }
        }
        return ans;
    }
    void process(int i,int j){
        visited[i][j] = true;
        for(auto el:adj(i,j)){
            if(visited[el.first][el.second])
                continue;
            // cout<<el.first<<" "<<el.second<<endl;
            q.push(el);
        }
    }
public:
    int shortestPathBinaryMatrix(vector<vector<int>>& grid) {
        if(grid[0][0]==1) return -1;
        this -> grid = grid;
        n = grid.size();
        visited = vector<vector<bool>>(n,vector<bool>(n,false));
        q.push({0,0});
        int pop = 1;
        int val  = 1;
        while(pop){
            while(pop--){
                auto node = q.front();
                if(!visited[node.first][node.second]){
                    // cout<<node.first<<" "<<node.second<<endl;
                    process(node.first,node.second);
                }
                if(node.first == n-1 && node.second == n-1){
                    return val;
                }
                q.pop();
            }
            pop = q.size();
            val++;
        }
        return -1;
    }
};
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