<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 ans = 0;
    bool vstd[105][105];

    vector<pair<int,int>> pth = {{1,0},{-1,0},{0,1},{0,-1}};
    
    bool isValid(int l , int k , int n , int m){
        if(l>=0 && l<n && k>=0 && k<m && vstd[l][k] == false) {
            return true;
        }
        return false;
    }

    void DFS(vector<vector<int>>& grid , int si , int sj , int n , int m){
        queue<pair<int,int>> qu;
        qu.push({si,sj});
        vstd[si][sj] = true;
        
        while(!qu.empty()){
            pair<int,int> a = qu.front();
            int ai = a.first;
            int aj = a.second;
            qu.pop();


            for(auto crnt: pth){
                int ni = ai + crnt.first;
                int nj = aj + crnt.second;

                if(ni < 0 || ni >= n || nj < 0 || nj >= m || grid[ni][nj] == 0){
                    ans++;
                }
                
                if(isValid(ni,nj,n,m) && grid[ni][nj] == 1){
                    vstd[ni][nj] = true;
                    qu.push({ni,nj});
                }
            }

        }
    }

    int islandPerimeter(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();

        int i , j;

        for(i=0 ; i<n ; i++){
            for(j=0 ; j<m ; j++){
                if(grid[i][j] == 1 && vstd[i][j] == false){
                    DFS(grid,i,j,n,m);
                    break;
                }
            }
        }

        return ans;
    }
};
81932