Problem11.java

import java.io.*;
import java.util.*;

public class Problem11 {
	private static final int GRID_SIZE = 20;
	private static final int PROD_LEN = 4;
	private static final int GRID_BUFF = GRID_SIZE - PROD_LEN;

	private static final String gridStr = 
	"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";

	public static void main(String[] args) {
		new Problem11().solve();
	}
	
	public void solve() {
		int[][] gridArray = parseGrid();
		
		int prod = 1;
		int maxProd = Integer.MIN_VALUE;
		
		for (int i = 0; i < gridArray.length; i++) {
			for (int j = 0; j < gridArray[i].length; j++) {
				if (gridArray[i][j] == 0) {
					continue;
				}
				
				// test right
				if (j <= GRID_BUFF) {
					prod = 1;
					for (int k = 0; k < PROD_LEN; k++)
						prod *= gridArray[i][j+k];
					
					if (prod > maxProd) maxProd = prod;
				}
				
				// test down
				if (i <= GRID_BUFF) {
					prod = 1;
					for (int k = 0; k < PROD_LEN; k++)
						prod *= gridArray[i+k][j];
					
					if (prod > maxProd) maxProd = prod;
				}
				
				// test diagonal left down
				if (i <= GRID_BUFF && j >= PROD_LEN - 1) {
					prod = 1;
					for (int k = 0; k < PROD_LEN; k++)
						prod *= gridArray[i+k][j-k];
					
					if (prod > maxProd) maxProd = prod;
				}
				
				// test diagonal right down
				if (i <= GRID_BUFF && j <= GRID_BUFF) {
					prod = 1;
					for (int k = 0; k < PROD_LEN; k++)
						prod *= gridArray[i+k][j+k];
					
					if (prod > maxProd) maxProd = prod;
				}
				
			}
		}
		
		System.out.println("The maximum product is " + maxProd);
	}
	
	public int[][] parseGrid() {
		int[][] gridArray = new int[GRID_SIZE][GRID_SIZE];
				
		Scanner scanner = new Scanner(gridStr);
		
		int i = 0, j = 0;
		while (scanner.hasNextInt()) {
			gridArray[i++ / 20][j++ % 20] = scanner.nextInt();
		}
		
		return gridArray;
	}
}