<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 n,m;
    bool vis[105][105];
    int ans = 0;
    vector<pair<int,int>> d={{1,0},{-1,0},{0,1},{0,-1}};
    bool valid(int i, int j)
    {
        return i >= 0 && i < n && j >= 0 && j < m;
    }
    void dfs(int si, int sj, vector<vector<int>> &grid)
    {
        vis[si][sj] = true;
        for(int i = 0; i < 4; i++)
        {
            int ci = si + d[i].first;
            int cj = sj + d[i].second;
            if(!valid(ci,cj)) ans++;
            else
                if(grid[ci][cj] == 0) ans++;
            if(valid(ci,cj) && !vis[ci][cj] && grid[ci][cj] == 1)
            {
                dfs(ci,cj,grid);
            }
        }
    }
    int islandPerimeter(vector<vector<int>>& grid) {
        memset(vis, false, sizeof(vis));
        n = grid.size();
        m = grid[0].size();
        for(int i = 0; i < n; i++)
        {
            for(int j = 0; j < m; j++)
            {
                if(!vis[i][j] && grid[i][j] == 1)
                {
                    dfs(i,j,grid);
                }
            }
        }
        return ans;
    }
};
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