# LeetCode - 0892. Surface Area of 3D Shapes
### 題目網址：https://leetcode.com/problems/surface-area-of-3d-shapes/
###### tags: `LeetCode` `Easy` `數學` `幾何`

/*
    -LeetCode format-
    Problem: 892. Surface Area of 3D Shapes
    Difficulty: Easy
    
    by Inversionpeter
*/



class Solution {
public:
    int surfaceArea(vector<vector<int>>& grid) {
        int area = 0, dx[4] = { 0, 1, 0, -1 }, dy[4] = { -1, 0, 1, 0 }, newX, newY;
        for (int i = 0; i != grid.size(); ++i)
            for (int j = 0; j != grid[0].size(); ++j)
                if (grid[i][j]) {
                    for (int k = 0; k < 4; ++k) {
                        newX = j + dx[k]; newY = i + dy[k];
                        if (newX < 0 || newX == grid[0].size() || newY < 0 || newY == grid.size())
                            area += grid[i][j];
                        else if (grid[i][j] > grid[newY][newX])
                            area += grid[i][j] - grid[newY][newX];
                    }
                    area += 2;
                }
        return area;
    }
};