ProjectEulerを斬る！問11

Problem 11
22 February 2002

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 any direction (up, down, left, right, or diagonally) in the 20×20 grid?

下も20*20の格子を示しました。4つの同一斜線部分の数字を赤で示しています。
これらの数字の積は26 × 63 × 78 × 14 = 1788696です。
どのような方向(縦、横、斜め)でもよいので、この20*20の格子の中で隣り合う4つの数字の積のなかで、最も大きくなるものを求めなさい。(日本語訳PNN)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
string note;
note  = "08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08 ";
note += "49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00 ";
note += "81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65 ";
note += "52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91 ";
note += "22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80 ";
note += "24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50 ";
note += "32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70 ";
note += "67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21 ";
note += "24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72 ";
note += "21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95 ";
note += "78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92 ";
note += "16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57 ";
note += "86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58 ";
note += "19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40 ";
note += "04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66 ";
note += "88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69 ";
note += "04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36 ";
note += "20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16 ";
note += "20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54 ";
note += "01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48 ";

int[,] grid = new int[20,20];
for (int i = 0; i<= 19; i++)
{
for (int j = 0; j <= 19; j++)
{
grid[j,i] = int.Parse(note.Substring(j*3 + i*60, 2));
}
}

int max = 0;
int cal = 0;
for (int i = 0; i <= 19; i++)
{
for (int j = 0; j <= 19; j++)
{
if (19 - j - 3 >= 0)
{
cal = grid[j, i] * grid[j + 1, i] * grid[j + 2, i] * grid[j + 3, i];
if (cal >= max)
{
max = cal;
}
}
if (19 - i - 3 >= 0)
{
cal = grid[j, i] * grid[j, i + 1] * grid[j, i + 2] * grid[j, i + 3];
if (cal >= max)
{
max = cal;
}
}
if (19 - i - 3 >= 0 && 19 - j - 3 >= 0)
{
cal = grid[j, i] * grid[j + 1, i + 1] * grid[j + 2, i + 2] * grid[j + 3, i + 3];
if (cal >= max)
{
max = cal;
}
}
if (19 - i - 3 >= 0 && j >= 3)
{
cal = grid[j, i] * grid[j -1, i + 1] * grid[j - 2, i + 2] * grid[j - 3, i + 3];
if (cal >= max)
{
max = cal;
}
}
}
}
Console.WriteLine(max);
Console.ReadLine();
}
}
}

出力結果：70600674