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.
题目给出了一个方阵，方阵里面的数值是柱子的高度，求三视图所有的阴影部分的面积。俯视图投影就是不为0的柱子的个数，主视图、侧视图是当前视图柱子的最高值求和。
class Solution:
def projectionArea(self, grid):
"""
:type grid: List[List[int]]
:rtype: int
"""
top, front, side = 0, 0, 0
l = len(grid)
for i in range(l):
x, y = 0, 0
for j in range(l):
if grid[i][j] != 0:
top += 1
x = max(x, grid[i][j])
y = max(y, grid[j][i])
front += x
side += y
return top + front + side
LeetCode 883 Projection Area of 3D Shapes 解题报告
原文：https://www.cnblogs.com/yao1996/p/10347654.html