main.py

#!/usr/bin/env python3

# https://www.hackerrank.com/challenges/alphabet-rangoli/problem

import math

# ----c----
# --c-b-c--
# c-b-a-b-c
# --c-b-c--
# ----c----

size = 26
rows = 2 * size - 1
cols = 2 * rows - 1

neihbors = [
    (-1,  0),  # left
    ( 1,  0),  # right
    ( 0, -2),  # up
    ( 0,  2)   # down
]

canvas = [['-'] * cols for _ in range(rows)]

start_row = rows // 2
start_col = cols // 2
canvas[start_row][start_col] = 'a'

wave = [(rows // 2, cols // 2)]

for _ in range(size - 1):
    new_wave = []

    for (row0, col0) in wave:
        for (drow, dcol) in neihbors:
            row = row0 + drow
            col = col0 + dcol
            if 0 <= row < rows and 0 <= col < cols:
                if canvas[row][col] == '-':
                    canvas[row][col] = chr(ord(canvas[row0][col0]) + 1)
                    new_wave.append((row, col))

    wave = new_wave

for row in canvas:
    print("".join(row))