/* 
 * Solution to Project Euler problem 11
 * Copyright (c) Project Nayuki. All rights reserved.
 * 
 * https://www.nayuki.io/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p011 implements EulerSolution {
	
	public static void main(String[] args) {
		System.out.println(new p011().run());
	}
	
	
	/* 
	 * We visit each grid cell and compute the product in the 4 directions starting from that cell.
	 * Note that the maximum product is 99^4 = 96059601, which fits in a Java int type.
	 */
	private static final int CONSECUTIVE = 4;
	
	public String run() {
		int max = -1;
		for (int y = 0; y < SQUARE.length; y++) {
			for (int x = 0; x < SQUARE[y].length; x++) {
				max = Math.max(product(x, y, 1,  0, CONSECUTIVE), max);
				max = Math.max(product(x, y, 0,  1, CONSECUTIVE), max);
				max = Math.max(product(x, y, 1,  1, CONSECUTIVE), max);
				max = Math.max(product(x, y, 1, -1, CONSECUTIVE), max);
			}
		}
		return Integer.toString(max);
	}
	
	
	private static int product(int x, int y, int dx, int dy, int n) {
		// First endpoint is assumed to be in bounds. Check if second endpoint is in bounds.
		if (!isInBounds(x + (n - 1) * dx, y + (n - 1) * dy))
			return -1;
		
		int prod = 1;
		for (int i = 0; i < n; i++, x += dx, y += dy)
			prod *= SQUARE[y][x];
		return prod;
	}
	
	
	private static boolean isInBounds(int x, int y) {
		return 0 <= y && y < SQUARE.length && 0 <= x && x < SQUARE[y].length;
	}
	
	
	private static int[][] SQUARE = {
		{ 8, 2,22,97,38,15, 0,40, 0,75, 4, 5, 7,78,52,12,50,77,91, 8},
		{49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48, 4,56,62, 0},
		{81,49,31,73,55,79,14,29,93,71,40,67,53,88,30, 3,49,13,36,65},
		{52,70,95,23, 4,60,11,42,69,24,68,56, 1,32,56,71,37, 2,36,91},
		{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, 3,45, 2,44,75,33,53,78,36,84,20,35,17,12,50},
		{32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70},
		{67,26,20,68, 2,62,12,20,95,63,94,39,63, 8,40,91,66,49,94,21},
		{24,55,58, 5,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72},
		{21,36,23, 9,75, 0,76,44,20,45,35,14, 0,61,33,97,34,31,33,95},
		{78,17,53,28,22,75,31,67,15,94, 3,80, 4,62,16,14, 9,53,56,92},
		{16,39, 5,42,96,35,31,47,55,58,88,24, 0,17,54,24,36,29,85,57},
		{86,56, 0,48,35,71,89, 7, 5,44,44,37,44,60,21,58,51,54,17,58},
		{19,80,81,68, 5,94,47,69,28,73,92,13,86,52,17,77, 4,89,55,40},
		{ 4,52, 8,83,97,35,99,16, 7,97,57,32,16,26,26,79,33,27,98,66},
		{88,36,68,87,57,62,20,72, 3,46,33,67,46,55,12,32,63,93,53,69},
		{ 4,42,16,73,38,25,39,11,24,94,72,18, 8,46,29,32,40,62,76,36},
		{20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74, 4,36,16},
		{20,73,35,29,78,31,90, 1,74,31,49,71,48,86,81,16,23,57, 5,54},
		{ 1,70,54,71,83,51,54,69,16,92,33,48,61,43,52, 1,89,19,67,48},
	};
	
}