<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 row,col,perimeter;
    bool vis[100][100];
    vector<pair<int,int>>d={{0,-1},{0,1},{-1,0},{1,0}};

    bool valid(int i,int j){
        return 0<=i&&i<row&&0<=j&&j<col;
    }

    void dfs(int i,int j,vector<vector<int>>&grid){
        vis[i][j]=true;
        for(int it=0;it<4;it++){
            int ii=i+d[it].first,jj=j+d[it].second;
            if(!valid(ii,jj)||(valid(ii,jj)&&!grid[ii][jj]))perimeter++;
            if(valid(ii,jj)&&!vis[ii][jj]&&grid[ii][jj])dfs(ii,jj,grid);
        }
    }

    int islandPerimeter(vector<vector<int>>& grid) {
        row=grid.size(),col=grid[0].size();
        memset(vis,false,sizeof(vis));
        perimeter=0;
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                if(!vis[i][j]&&grid[i][j])dfs(i,j,grid);
            }
        }
        return perimeter;
    }
};

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