3D surface area | : carlos labs :

Hackerrank Challenges - 3D surface area

(CM) I love this problem. I used it for teaching and visualising 3D arrays -I included "counting the voxels" as part of my implementation, as I explained this to the audience.

There are two parts to the problem: the transformation of a series of 2D arrays into a cube structure, and the actual counting of the faces of every "voxel" in the 3D cube.

This is not a "pythonic solution" - if any such thing exists: code either solves a problem, or it doesn't.

# Complete the surfaceArea function below.
def surfaceArea(A):
    aCube = []
    Z = 0
    dMax = 0
    faces = 0
    voxels = 0

# 1) find max height in each array for creating the cube
    for i in range(H):
        for j in range(W):
            dMax = A[i][j]
            if (dMax > Z):
                Z = dMax

# 2) create empty cube
    for iC in range(H):
        aCube.append([])
        for jC in range(W):
            aCube[iC].append([])
            for k in range(Z):
                aCube[iC][jC].append(0)

# 3) read 2d matrix into 3d cube: fill "solid" voxels with "1"
    for i in range(H):
        for j in range(W):
            for k in range(A[i][j]):
                aCube[i][j][k]=1

# 4) scan every voxel for neighbours
    for i in range(H):      
        for j in range(W):
            iPrev = jPrev = kPrev = 0                           
            iPost = jPost = kPost = 0                                         
            for k in range(Z):
                if (aCube[i][j][k]==1):
                    voxels = voxels + 1
                    iPrev = iPrev - 1
                    jPrev = jPrev - 1                         
                    kPrev = kPrev - 1                            
                    iPost = i + 1
                    jPost = j + 1
                    kPost = k + 1
                    if (iPrev < 0):
                        faces+=1
                    else:
                        if (aCube[iPrev][j][k]==0):
                            faces+=1
                    if (jPrev < 0):
                        faces+=1
                    else:
                        if (aCube[i][jPrev][k]==0):
                            faces+=1                        
                    if (kPrev < 0):
                        faces+=1 
                    else:
                        if (aCube[i][j][kPrev]==0):
                            faces+=1 
                    # next voxel up                                                   
                    if (iPost >= H):
                        faces+=1
                    else:
                        if (aCube[iPost][j][k]==0):
                            faces+=1
                        else:
                            if (aCube[iPost][j][k]==1):
                                faces=faces-1
                    if (jPost >= W):
                        faces+=1
                    else:
                        if (aCube[i][jPost][k]==0):
                            faces+=1
                        else:
                            if (aCube[i][jPost][k]==1):
                                faces=faces-1                          
                    if (kPost >= Z):
                        faces+=1
                    else:
                        if (aCube[i][j][kPost]==0):
                            faces+=1
                        else:
                            if (aCube[i][j][kPost]==1):
                                faces=faces-1

## return 'voxels: ',str(voxels),' faces:', str(faces)
    return faces