<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 sum;
    bool check(vector<vector<int>>& grid, int i, int j){
         if(i>-1 && i<grid.size() && j >-1 &&j<grid[0].size() && grid[i][j]==1)
             return true;
         return false;
        
    }
    
    bool check2(vector<vector<int>>& grid, int i, int j){
         if(i>-1 && i<grid.size() && j >-1 &&j<grid[0].size() && grid[i][j])
             return true;
         return false;
        
    }
    
    
    
    void compute_sum(vector<vector<int>>& grid, int i, int j){
        sum++;
        grid[i][j]++;
        if(check(grid,i+1,j)){
           
            compute_sum(grid,i+1,j);
        }
        if(check(grid,i-1,j)){

            compute_sum(grid,i-1,j);
        }
        if(check(grid,i,j+1)){
            compute_sum(grid,i,j+1);
        }
        if(check(grid,i,j-1)){
            compute_sum(grid,i,j-1);
        }
           
    }
    
    
    int islandPerimeter(vector<vector<int>>& grid) {
        
        sum = 0;
        
        for(int i=0;i<grid.size();i++){
            for(int j=0;j<grid[0].size();j++){
                if(grid[i][j]==1){
                    compute_sum(grid, i,j);
                }
            }
        }
        
        int ans = sum*4;
        int minus_ans = 0;
        
        for(int i=0;i<grid.size();i++){
            for(int j=0;j<grid[0].size();j++){
                if(grid[i][j]){
                    if(check2(grid,i,j-1))
                        minus_ans++;
                    if(check2(grid,i,j+1))
                        minus_ans++;
                    if(check2(grid,i-1,j))
                        minus_ans++;
                    if(check2(grid,i+1,j))
                        minus_ans++;
                }
            }
        }   
        
        
        return ans - minus_ans;
        
        
        
        
        
        
        
        
        
        
        
        
    }
};
20552