Discussion on 3D Surface Area Challenge

8 years ago+ 11 comments

For every element in the matrix, it adds top and bottom area (which are 1 unit each one), and then, for each side of every element, the area from top of the element to top of their neighbours.

For instance, in this example:

0 1 0
2 4 2
0 0 0

Analyzing the element '1' it will add 2 units to the area (top and bottom squares) and 1 unit for north, east and west sides (no unit at south because 4 is larger than 1). Then, for instance at element 4 it will add 2 units (top and bottom units), then 3 units at north (4-1), 2 units at east and west (4-2) and 4 units at south (4-0).

Python version:

def surfaceArea(A):
    area = 0
    neighs = [[-1, 0], [0, 1], [1, 0], [0, -1]]

    for x in range(H):
        for y in range(W):
            el = A[x][y]
            # add base and top area
            area += 2
            for dx, dy in neighs:
                try:
                    # Raise index exception if trying to access index -1
                    if -1 in [x+dx, y+dy]:
                        raise IndexError

                    # Add area of actual element from neighbours as base
                    new = el - A[x+dx][y+dy]
                    if new > 0:
                        area += new
                # Add area corresponding to the sides of the figure
                except IndexError:
                    area += el

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