e11.py

#!/usr/bin/env python3

'''
In the 20×20 grid below, four numbers along a diagonal line have been marked
in red.

08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48

The product of these numbers is 26 × 63 × 78 × 14 = 1788696.

What is the greatest product of four adjacent numbers in the same direction
(up, down, left, right, or diagonally) in the 20×20 grid?
'''
import itertools

def mul(iterable):
    total = 1
    for i in iterable:
        total *= i
    return total

def main():
    grid_text = (
    "08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08 "
    "49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00 "
    "81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65 "
    "52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91 "
    "22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80 "
    "24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50 "
    "32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70 "
    "67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21 "
    "24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72 "
    "21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95 "
    "78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92 "
    "16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57 "
    "86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58 "
    "19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40 "
    "04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66 "
    "88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69 "
    "04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36 "
    "20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16 "
    "20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54 "
    "01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48 "
    )
    grid = [int(i) for i in grid_text.strip().split(" ")]
    size = 20
    block = 4

    bars = []
    # Horizontal and vertical
    for i in range(size):
        rows = grid[size*i : size*(i+1)]
        bars.append(rows)
        cols = grid[i : size*size : size]
        bars.append(cols)
    # Diagonal (left to right)
    for i in range(size):
        diag1 = grid[i : size*(size-i) : size+1]
        diag2 = grid[size*(i+1) : size*size-i : size+1] # for i==size-1 gives []
        bars.append(diag1)
        bars.append(diag2)
    # Diagonal (right to left)
    for i in range(size-1, -1, -1):
        diag3 = grid[i : (size*i)+1 : size-1]
        diag4 = grid[size*size - 1 - size*i : size*size - i: size-1]
        bars.append(diag3)
        bars.append(diag4)
    # Remove short bars
    bars = [b for b in bars if len(b) >= block]
    # Find all products in all bars
    combinations = []
    for b in bars:
        for i in range((size+1)-block):
            combinations.append(itertools.islice(b, i, i+block))
    result = max(map(mul, combinations))
    print('Result: ', result)

if __name__ == '__main__':
    main()