[LeetCode]#883. Projection Area of 3D Shapes

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:

1. Calculate xy-plane.
2. Calculate yz-plane.
3. Calculate xz-plane.
4. 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

Submissions:

Reference:

Python numpy implementation - LeetCode Discuss

[LeetCode] 883. Projection Area of 3D Shapes

np.max(等價於np.amax)用法

https://iter01.com/557354.html