Main.java

/*
@author: mc-es

Problem 11
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?

Answer: 70600674
*/

public class Main {
	public static void main(String[] args) {
		String gridString = """
				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
				 """;

		int[][] grid = new int[20][20];
		String[] rows = gridString.strip().split("\n");

		for (int i = 0; i < rows.length; i++) {
			String[] nums = rows[i].split(" ");
			for (int j = 0; j < nums.length; j++) {
				grid[i][j] = Integer.parseInt(nums[j]);
			}
		}

		int greatestProduct = 0;

		// Check horizontally
		for (int i = 0; i < grid.length; i++) {
			for (int j = 0; j < grid[0].length - 3; j++) {
				int[] numbers = { grid[i][j], grid[i][j + 1], grid[i][j + 2], grid[i][j + 3] };
				int p = product(numbers);
				if (p > greatestProduct) {
					greatestProduct = p;
				}
			}
		}

		// Check vertically
		for (int i = 0; i < grid.length - 3; i++) {
			for (int j = 0; j < grid[0].length; j++) {
				int[] numbers = { grid[i][j], grid[i + 1][j], grid[i + 2][j], grid[i + 3][j] };
				int p = product(numbers);
				if (p > greatestProduct) {
					greatestProduct = p;
				}
			}
		}

		// Check diagonally (top-left to bottom-right)
		for (int i = 0; i < grid.length - 3; i++) {
			for (int j = 0; j < grid[0].length - 3; j++) {
				int[] numbers = { grid[i][j], grid[i + 1][j + 1], grid[i + 2][j + 2], grid[i + 3][j + 3] };
				int p = product(numbers);
				if (p > greatestProduct) {
					greatestProduct = p;
				}
			}
		}

		// Check diagonally (bottom-left to top-right)
		for (int i = 3; i < grid.length - 3; i++) {
			for (int j = 0; j < grid[0].length - 3; j++) {
				int[] numbers = { grid[i][j], grid[i - 1][j + 1], grid[i - 2][j + 2], grid[i - 3][j + 3] };
				int p = product(numbers);
				if (p > greatestProduct) {
					greatestProduct = p;
				}
			}
		}

		System.out.println(greatestProduct);
	}

	public static int product(int[] numbers) {
		int result = 1;
		for (int i = 0; i < numbers.length; i++) {
			result *= numbers[i];
		}
		return result;
	}

}