<p>You are given an <code>m x n</code> matrix <code>maze</code> (<strong>0-indexed</strong>) with empty cells (represented as <code>&#39;.&#39;</code>) and walls (represented as <code>&#39;+&#39;</code>). You are also given the <code>entrance</code> of the maze, where <code>entrance = [entrance<sub>row</sub>, entrance<sub>col</sub>]</code> denotes the row and column of the cell you are initially standing at.</p>

<p>In one step, you can move one cell <strong>up</strong>, <strong>down</strong>, <strong>left</strong>, or <strong>right</strong>. You cannot step into a cell with a wall, and you cannot step outside the maze. Your goal is to find the <strong>nearest exit</strong> from the <code>entrance</code>. An <strong>exit</strong> is defined as an <strong>empty cell</strong> that is at the <strong>border</strong> of the <code>maze</code>. The <code>entrance</code> <strong>does not count</strong> as an exit.</p>

<p>Return <em>the <strong>number of steps</strong> in the shortest path from the </em><code>entrance</code><em> to the nearest exit, or </em><code>-1</code><em> if no such path exists</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/06/04/nearest1-grid.jpg" style="width: 333px; height: 253px;" />
<pre>
<strong>Input:</strong> maze = [[&quot;+&quot;,&quot;+&quot;,&quot;.&quot;,&quot;+&quot;],[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;+&quot;],[&quot;+&quot;,&quot;+&quot;,&quot;+&quot;,&quot;.&quot;]], entrance = [1,2]
<strong>Output:</strong> 1
<strong>Explanation:</strong> There are 3 exits in this maze at [1,0], [0,2], and [2,3].
Initially, you are at the entrance cell [1,2].
- You can reach [1,0] by moving 2 steps left.
- You can reach [0,2] by moving 1 step up.
It is impossible to reach [2,3] from the entrance.
Thus, the nearest exit is [0,2], which is 1 step away.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/06/04/nearesr2-grid.jpg" style="width: 253px; height: 253px;" />
<pre>
<strong>Input:</strong> maze = [[&quot;+&quot;,&quot;+&quot;,&quot;+&quot;],[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;],[&quot;+&quot;,&quot;+&quot;,&quot;+&quot;]], entrance = [1,0]
<strong>Output:</strong> 2
<strong>Explanation:</strong> There is 1 exit in this maze at [1,2].
[1,0] does not count as an exit since it is the entrance cell.
Initially, you are at the entrance cell [1,0].
- You can reach [1,2] by moving 2 steps right.
Thus, the nearest exit is [1,2], which is 2 steps away.
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/06/04/nearest3-grid.jpg" style="width: 173px; height: 93px;" />
<pre>
<strong>Input:</strong> maze = [[&quot;.&quot;,&quot;+&quot;]], entrance = [0,0]
<strong>Output:</strong> -1
<strong>Explanation:</strong> There are no exits in this maze.
</pre>

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

<ul>
	<li><code>maze.length == m</code></li>
	<li><code>maze[i].length == n</code></li>
	<li><code>1 &lt;= m, n &lt;= 100</code></li>
	<li><code>maze[i][j]</code> is either <code>&#39;.&#39;</code> or <code>&#39;+&#39;</code>.</li>
	<li><code>entrance.length == 2</code></li>
	<li><code>0 &lt;= entrance<sub>row</sub> &lt; m</code></li>
	<li><code>0 &lt;= entrance<sub>col</sub> &lt; n</code></li>
	<li><code>entrance</code> will always be an empty cell.</li>
</ul>

class Solution {
public:
    int nearestExit(vector<vector<char>>& maze, vector<int>& entrance) {
        // mark entrance as 'x'
        maze[entrance[0]][entrance[1]] = 'x';

        int m = maze.size();
        int n = maze[0].size();

        queue<vector<int>> current_step_queue;
        mark_adjacent_spots(maze, entrance[0], entrance[1], current_step_queue, m, n);

        bool found_exit = false;
        int num_steps = 0;

        while ( (current_step_queue.empty() == false) && (found_exit == false) )
        {
            num_steps++;
            uint16_t step_x_q_len = current_step_queue.size();
            for (size_t i = 0; (i < step_x_q_len) && (!found_exit); i++)
            {
                vector<int> current_spot = current_step_queue.front();
                current_step_queue.pop();
                if (is_exit(current_spot[0], current_spot[1], m, n))
                {
                    found_exit = true;
                }
                else
                {
                    mark_adjacent_spots(maze, current_spot[0], current_spot[1], current_step_queue, m, n);
                }
            }
        }

        if ( found_exit == true)
        {
            return num_steps;
        }
        else
        {
            return -1;
        }


    }

    void mark_adjacent_spots(vector<vector<char>>& maze, int curr_row, int curr_column, queue<vector<int>>& queue, int m, int n)
    {
        vector<int> new_spot;

        // up 
        if ((curr_row -1) >= 0)
        {
            if (maze[curr_row - 1][curr_column] == '.')
            {
                maze[curr_row - 1][curr_column] = 'x';
                new_spot = {curr_row - 1, curr_column};
                queue.push(new_spot);
            }
        }
        // down
        if ( (curr_row + 1) < m)
        {
            if (maze[curr_row + 1][curr_column] == '.')
            {
                maze[curr_row + 1][curr_column] = 'x';
                new_spot = {curr_row + 1, curr_column};
                queue.push(new_spot);
            }
        }

        // left
        if ( (curr_column - 1) >= 0)
        {
            if (maze[curr_row][curr_column - 1] == '.')
            {
                maze[curr_row][curr_column - 1] = 'x';
                new_spot = {curr_row, curr_column - 1};
                queue.push(new_spot);
            }
        }

        // right
        if ( (curr_column + 1) < n)
        {
            if (maze[curr_row][curr_column + 1] == '.')
            {
                maze[curr_row][curr_column + 1] = 'x';
                new_spot = {curr_row, curr_column + 1};
                queue.push(new_spot);
            }
        }
    }

        bool is_exit(int row, int column, int m, int n)
    {
        bool is_exit = false;
        if ( (row == 0) || (row == m-1) )
        {
            is_exit = true;
        }
        else if ( (column == 0) || (column == n-1) )
        {
            is_exit = true;
        }
        return is_exit;
    }
};
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