[leetcode] 883. Projection Area of 3D Shapes

[leetcode] 883. Projection Area of 3D Shapes

Description

On a N * N grid, we place some 1 * 1 * 1 cubes that are axis-aligned with the x, y, and z axes.

Each value v = grid[i][j] represents a tower of v cubes placed on top of grid cell (i, j).

Now we view the projection of these cubes onto the xy, yz, and zx planes.

A projection is like a shadow, that maps our 3 dimensional figure to a 2 dimensional plane.

Here, we are viewing the “shadow” when looking at the cubes from the top, the front, and the side.

Return the total area of all three projections.

Example 1:

Input: [[2]]Output: 5

Example 2:

Input: [[1,2],[3,4]]Output: 17Explanation: Here are the three projections ("shadows") of the shape made with each axis-aligned plane.

Example 3:

Input: [[1,0],[0,2]]Output: 8

Example 4:

Input: [[1,1,1],[1,0,1],[1,1,1]]Output: 14

Example 5:

Input: [[2,2,2],[2,1,2],[2,2,2]]Output: 21

Note:

1 <= grid.length = grid[0].length <= 500 <= grid[i][j] <= 50

分析

题目的意思是：给定一个N*N的网格，网格里面的数代表三维坐标下的z，网格的行和列代表x,y。求主视图，左视图，俯视图的面积。

这道题的俯视图很简单，就是N*N的网格中有数的格子数。左视图是网格中每一行遍历的最大值主石图是网格中每一列遍历的最大值

如果知道这些就好办了，写两个循环遍历一下就知道了。

代码

class Solution: def projectionArea(self, grid: List[List[int]]) -> int: res=0 N=len(grid) for i in range(N): max_col=0 max_row=0 for j in range(N): if(grid[i][j]): res+=1 max_row=max(max_row,grid[i][j]) max_col=max(max_col,grid[j][i]) res+=max_col+max_row return res

参考文献

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