<p>You are given <code>row x col</code> <code>grid</code> representing a map where <code>grid[i][j] = 1</code> represents&nbsp;land and <code>grid[i][j] = 0</code> represents water.</p>

<p>Grid cells are connected <strong>horizontally/vertically</strong> (not diagonally). The <code>grid</code> is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells).</p>

<p>The island doesn&#39;t have &quot;lakes&quot;, meaning the water inside isn&#39;t connected to the water around the island. One cell is a square with side length 1. The grid is rectangular, width and height don&#39;t exceed 100. Determine the perimeter of the island.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img src="https://assets.leetcode.com/uploads/2018/10/12/island.png" style="width: 221px; height: 213px;" />
<pre>
<strong>Input:</strong> grid = [[0,1,0,0],[1,1,1,0],[0,1,0,0],[1,1,0,0]]
<strong>Output:</strong> 16
<strong>Explanation:</strong> The perimeter is the 16 yellow stripes in the image above.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> grid = [[1]]
<strong>Output:</strong> 4
</pre>

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

<pre>
<strong>Input:</strong> grid = [[1,0]]
<strong>Output:</strong> 4
</pre>

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

<ul>
	<li><code>row == grid.length</code></li>
	<li><code>col == grid[i].length</code></li>
	<li><code>1 &lt;= row, col &lt;= 100</code></li>
	<li><code>grid[i][j]</code> is <code>0</code> or <code>1</code>.</li>
	<li>There is exactly one island in <code>grid</code>.</li>
</ul>

class Solution {
public:
    int islandPerimeter(vector<vector<int>>& grid) {
        int m = grid.size(), n = grid[0].size();

        // Find first island tile
        int i = 0, j = 0;
        while(i < m) {
            if(grid[i][j])
                break;
            
            j++;
            if(j == n) {
                j = 0;
                i++;
            }
        }

        // No island found
        if(i == m)
            return 0;
        
        queue<pair<int, int>> toVisit;
        vector<vector<bool>> visited(m, vector<bool>(n, false));
        visited[i][j] = true;
        toVisit.push({i, j});
        int perimeter = 0;
        while(!toVisit.empty()) {
            auto [i, j] = toVisit.front();
            toVisit.pop();
//            cout << "On [" << i << ", " << j << "]... ";

            // Perimeter is the number of sides that are water
            if(i == 0 || !grid[i-1][j]) { // up
                perimeter++;
//                cout << "up ";
            }
            if(j == 0 || !grid[i][j-1]) { // left
                perimeter++;
//                cout << "left ";
            }
            if(i == m-1 || !grid[i+1][j]) { // down
                perimeter++;
//                cout << "down ";
            }
            if(j == n-1 || !grid[i][j+1]) { // right
                perimeter++;
//                cout << "right ";
            }
//            cout << endl;
            
            // Add surrounding unvisted nodes
            if(i > 0 && grid[i-1][j] && !visited[i-1][j]) { // up
                toVisit.push({i-1, j});
                visited[i-1][j] = true;
            }
            if(j > 0 && grid[i][j-1] && !visited[i][j-1]) { // left
                toVisit.push({i, j-1});
                visited[i][j-1] = true;
            }
            if(i < m-1 && grid[i+1][j] && !visited[i+1][j]) { // down
                toVisit.push({i+1, j});
                visited[i+1][j] = true;
            }
            if(j < n-1 && grid[i][j+1] && !visited[i][j+1]) { // right
                toVisit.push({i, j+1});
                visited[i][j+1] = true;
            }
        }

        return perimeter;
    }
};
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