[LeetCode]#883. Projection Area of 3D Shapes
2 min readJan 18, 2021
Environment: Python 3.8
Key technique: numpy, np, np.count_nonzero, np.amax
You are given an n x n grid where we place some 1 x 1 x 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 the cell (i, j).
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. 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: grid = [[1,2],[3,4]]
Output: 17
Explanation: Here are the three projections ("shadows") of the shape made with each axis-aligned plane.Analysis:
- Calculate xy-plane.
- Calculate yz-plane.
- Calculate xz-plane.
- Retrun xy + yz +xz result.
Solution:
import numpy as np
class Solution(object):
def projectionArea(self, grid):g_np = np.array(grid)
xy=np.count_nonzero(g_np)
xz=np.sum(np.amax(g_np, axis=0))
yz= np.sum(np.amax(g_np, axis=1))
return xy+yz+xz
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