<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 parameter;
    vector<pair<int,int>> d = {{1,0},{-1,0},{0,1},{0,-1}};

    bool valid(int i, int j, int n, int m){
        if(i<0 || i>=n || j<0 || j>=m) return false;
        return true;
    }

    void dfs(vector<vector<int>>& grid, vector<vector<bool>> &visited,int n, int m, int i, int j){
        visited[i][j] = true;
        if(grid[i][j] == 1){
            parameter += 4;
            for(pair<int,int> c:d){
                int ci = c.first+i;
                int cj = c.second+j;
                if(valid(ci,cj,n,m) && grid[ci][cj] == 1 && visited[ci][cj]){
                    parameter-=2;
                };
            }
        }
        for(pair<int,int> c:d){
            int ci = c.first+i;
            int cj = c.second+j;
            if(valid(ci,cj,n,m) && !visited[ci][cj]){
                dfs(grid,visited,n,m,ci,cj);
            }
        }
    }

    int islandPerimeter(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();
        vector<vector<bool>> visited(n, vector<bool> (m,false));
        parameter = 0;
        dfs(grid,visited,n,m,0,0);
        return parameter;
    }
};
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