<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 calc(int row,int col,vector<vector<int>>& grid){
        int total=4;
        
        int n = grid.size();
        int m = grid[0].size();
        if(row>=0 && row<n && (col-1) >= 0 && col < m && grid[row][col-1]==1)
            total--;
        if((row-1)>=0 && row<n && col >= 0 && col < m && grid[row-1][col]==1)
            total--;
        if(row>=0 && row<n && col >= 0 && (col+1) < m && grid[row][col+1]==1)
            total--;
        if(row>=0 && (row+1)<n && col >= 0 && col < m && grid[row+1][col]==1)
            total--;
        // cout<<row<<" "<<col<<" total="<<total<<endl;
        return total;
    }
    void bfs(int row, int col, vector<vector<int>>& vis,
             vector<vector<int>>& grid, int& ans) {
        vis[row][col] = 1;
        queue<pair<int, int>> q;
        int n = grid.size();
        int m = grid[0].size();
        ans+=calc(row,col,grid);
        q.push({row, col});
        int delRow[] = {-1, 0, +1, 0};
        int delCol[] = {0, +1, 0, -1};
        while (!q.empty()) {
            int nrow = q.front().first;
            int ncol = q.front().second;
            q.pop();
            for (int i = 0; i < 4; i++) {
                int grow = nrow + delRow[i];
                int gcol = ncol + delCol[i];
                if (grow >= 0 && grow < n && gcol >= 0 && gcol < m && grid[grow][gcol]==1 &&
                    !vis[grow][gcol]) {
                        ans+=calc(grow,gcol,grid);
                        vis[grow][gcol] = 1;
                    q.push({grow, gcol});
                }
            }
        }
    }
    int islandPerimeter(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();
        int ans = 0;
        vector<vector<int>> vis(n, vector<int>(m, 0));
        for (int row = 0; row < n; row++) {
            for (int col = 0; col < m; col++) {
                if (!vis[row][col] && grid[row][col] == 1) {
                    bfs(row, col, vis, grid, ans);
                }
            }
        }
        return ans;
    }
};
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