<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 {
    vector<int>dx={0,1,0,-1,0};
public:
    bool isValid(int i,int j,int n,int m){
        return i>=0 && j>=0 && i<n && j<m;
    }
    int dfs(int i,int j,vector<vector<int>>& grid,vector<vector<int>>& vis,int n,int m){
        if(!isValid(i,j,n,m))return 0;
        if(vis[i][j] || grid[i][j]==0)return 0;
        vis[i][j]=1;
        int ans = 4;
        for(int k=0;k<4;k++){
            int x = i+dx[k];
            int y = j+dx[k+1];
            if(isValid(x,y,n,m)){
                ans-=(grid[x][y]==1);
                ans+=dfs(x,y,grid,vis,n,m);
            }
        }
        return ans;
    }
    int islandPerimeter(vector<vector<int>>& grid) {
        int ans = 0;
        int n = grid.size();
        int m = grid[0].size();
        vector<vector<int>>vis(n,vector<int>(m,0));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                ans += dfs(i,j,grid,vis,n,m);
            }
        }
        return ans;
    }
};
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