<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 
{
private:
    struct Node
    {
        Node(int r, int c, Node* node) 
            : row{r}, 
              col{c}, 
              parent_node{node}
        {            
        }

        int row{0};
        int col{0};
        
        Node* parent_node{};
    };

private:
    void print_path(Node* cur_node)
    {
        while(cur_node->parent_node != nullptr)
        {
            std::cout << "[" << cur_node->row << " , " << cur_node->col << "]\n";

            cur_node = cur_node->parent_node;
        }

        // Print the source node.
        std::cout << "[" << cur_node->row << " , " << cur_node->col << "]\n";
    }

public:
    int shortestPathBinaryMatrix(vector<vector<int>>& grid) 
    {
        const int ROWS{static_cast<int>(grid.size())};
        const int COLS{static_cast<int>(grid[0].size())};

        int source_row {0};
        int source_col {0};
        int target_row {ROWS -1};
        int target_col {COLS -1};

        if( grid[source_row][source_col] == 1 ||
            grid[target_row][target_col] == 1)
        {
            return -1;
        }
        else if(source_row == target_row && 
                source_col == target_col)
        {
            return 1;
        }

        std::queue<Node*> coordinate_queue{};

        Node* source_node{new Node{source_row,source_col, nullptr}};

        coordinate_queue.emplace(source_node);

        std::vector<std::vector<int>> DIRECTIONS
        {            
            {0,1},
            {0,-1},
            {1,0},
            {1,1},
            {1,-1},
            {-1,0},
            {-1,1},
            {-1,-1},
        };
        const int NUM_DIRECTIONS{static_cast<int>(DIRECTIONS.size())};
        
        int result_length {0};
        while(!coordinate_queue.empty())
        {
            ++result_length;

            int num_nodes_at_cur_level{static_cast<int>(coordinate_queue.size())};
            while(num_nodes_at_cur_level--)
            {
                Node* parent_node = coordinate_queue.front();
                coordinate_queue.pop();
                
                int cur_row{parent_node->row};
                int cur_col{parent_node->col};

                if(cur_row == target_row &&
                   cur_col == target_col)
                {
                    // Print the path.
                    print_path(parent_node);

                    return result_length;
                }

                for(size_t dir_pos{0}; 
                    dir_pos < NUM_DIRECTIONS; 
                    ++dir_pos)
                {
                    int new_row {DIRECTIONS[dir_pos][0] + cur_row};
                    int new_col {DIRECTIONS[dir_pos][1] + cur_col};

                    if( new_row < 0 ||
                        new_col < 0 ||
                        new_row >= ROWS ||
                        new_col >= COLS ||
                        grid[new_row][new_col] == 1)
                    {
                        continue;
                    }

                    grid[new_row][new_col] = 1;

                    Node* new_node{new Node{new_row, new_col, parent_node}};

                    coordinate_queue.emplace(new_node);
                }
            }
        } // End of while()

        return -1;
    }
};

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