<p>You are given an <code>n x n</code> <code>grid</code> where you have placed some <code>1 x 1 x 1</code> cubes. Each value <code>v = grid[i][j]</code> represents a tower of <code>v</code> cubes placed on top of cell <code>(i, j)</code>.</p>

<p>After placing these cubes, you have decided to glue any directly adjacent cubes to each other, forming several irregular 3D shapes.</p>

<p>Return <em>the total surface area of the resulting shapes</em>.</p>

<p><strong>Note:</strong> The bottom face of each shape counts toward its surface area.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/08/tmp-grid2.jpg" style="width: 162px; height: 162px;" />
<pre>
<strong>Input:</strong> grid = [[1,2],[3,4]]
<strong>Output:</strong> 34
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/08/tmp-grid4.jpg" style="width: 242px; height: 242px;" />
<pre>
<strong>Input:</strong> grid = [[1,1,1],[1,0,1],[1,1,1]]
<strong>Output:</strong> 32
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/08/tmp-grid5.jpg" style="width: 242px; height: 242px;" />
<pre>
<strong>Input:</strong> grid = [[2,2,2],[2,1,2],[2,2,2]]
<strong>Output:</strong> 46
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>n == grid.length == grid[i].length</code></li>
	<li><code>1 &lt;= n &lt;= 50</code></li>
	<li><code>0 &lt;= grid[i][j] &lt;= 50</code></li>
</ul>

class Solution {
public:
    int surfaceArea(vector<vector<int>>& grid) {
        int ans=0, n=grid.size();
        for(int i=0; i<n; i++){
            for(int j=0; j<n; j++){
                if(grid[i][j]==0)   continue;
                int curr= 4*grid[i][j]+2;
                if(i>0) curr-=min(grid[i][j],grid[i-1][j]);
                if(j>0) curr-=min(grid[i][j],grid[i][j-1]);
                if(i<n-1) curr-=min(grid[i][j],grid[i+1][j]);
                if(j<n-1) curr-=min(grid[i][j],grid[i][j+1]);
                ans+=curr;
            }
        }
        return ans;
    }
};
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