Project Euler, problem 11 finalised

scratch_13.java

class Scratch {
    static long CURRENT_MAX = Long.MIN_VALUE;

    public static void main(String[] args) {
        int[][] grid = setupGrid();
        computeMaxProduct(grid);
        System.out.println(CURRENT_MAX);
    }

    private static void computeMaxProduct(int[][] grid) {
        // At each position, we've got to check, if we can:
        // - on the right
        // - down
        // - diagonal right
        // - diagonal left
        // This should cover all cases
        for (int i = 0; i < grid.length; i++) { // number of rows
            for (int j = 0; j < grid[i].length; j++) { // number of cols in current row
                if (weCanGoRight(grid[i].length, j)) {
                    computeMaxOnRight(grid, i, j);
                }
                if (weCanGoDown(grid.length, i)) {
                    computeMaxBelow(grid, i, j);
                }
                if (weCanGoDown(grid.length, i) && weCanGoRight(grid[i].length, j)) {
                    computeMaxDiagonalRight(grid, i, j);
                }
                if (weCanGoDown(grid.length, i) && weCanGoLeft(j)) {
                    computeMaxDiagonalLeft(grid, i, j);
                }
            }
        }
    }

    private static void computeMaxDiagonalLeft(int[][] grid, int row, int col) {
        long product = grid[row][col] * grid[row+1][col-1] * grid[row+2][col-2] * grid[row+3][col-3];
        if (product > CURRENT_MAX)
            CURRENT_MAX = product;
    }

    private static boolean weCanGoLeft(int currentColInRow) {
        return currentColInRow >= 3;
    }

    private static void computeMaxDiagonalRight(int[][] grid, int row, int col) {
        long product = grid[row][col] * grid[row+1][col+1] * grid[row+2][col+2] * grid[row+3][col+3];
        if (product > CURRENT_MAX)
            CURRENT_MAX = product;
    }

    private static void computeMaxBelow(int[][] grid, int row, int col) {
        long product = grid[row][col] * grid[row+1][col] * grid[row+2][col] * grid[row+3][col];
        if (product > CURRENT_MAX)
            CURRENT_MAX = product;
    }

    private static void computeMaxOnRight(int[][] grid, int row, int col) {
        long product = grid[row][col] * grid[row][col+1] * grid[row][col+2] * grid[row][col+3];
        if (product > CURRENT_MAX)
            CURRENT_MAX = product;
    }

    private static boolean weCanGoDown(int rows, int row) {
        //5 rows; max index: 4. Greatest index where we should return true: 1
        return rows >= row + 4;
    }

    private static boolean weCanGoRight(int colsInRow, int col) {
        // colsInRow = 5; greatest index: 4
        // return true if row index is at most: 1
        return colsInRow >= col + 4;
    }

    private static int[][] setupGrid() {
        int[][] grid = new int[][] {
                {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}
        };
        return grid;
    }
}