What is the greatest product of n adjacent numbers in the same direction (up, down, left, right, or diagonally) in given matrix?

greatest-product.php

<?php

/**
 * 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 the first four numbers is 8 × 2 × 22 × 97 = 34144.
 *
 * What is the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid?
 */

$array =
    [
        ['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'],
    ];

$rowMax = $colMax = 20;
$countMax = 4;
$greatestProduct = 0;

foreach($array as $row => $colArray) {
    foreach($colArray as $col => $value) {
        $forward = $downward = $diagnalRight = $diagonalLeft = 1;
        for($count = 0; $count < $countMax; $count++) {
            if($col+$count < $colMax) {
                $forward *= intval($array[$row][$col+$count]);
            }

            if($row+$count < $rowMax) {
                $downward *= intval($array[$row+$count][$col]);
            }

            if($col+$count < $colMax && $row+$count < $rowMax) {
                $diagnalRight *= intval($array[$row+$count][$col+$count]);
            }

            if($row+$count < $rowMax && $col-$count >= 0) {
                $diagonalLeft *= intval($array[$row+$count][$col-$count]);
            }
        }

        if($greatestProduct < $forward) {
            $greatestProduct = $forward;
        }

        if($greatestProduct < $downward) {
            $greatestProduct = $downward;
        }

        if($greatestProduct < $diagnalRight) {
            $greatestProduct = $diagnalRight;
        }

        if($greatestProduct < $diagonalLeft) {
            $greatestProduct = $diagonalLeft;
        }
    }
}

printf("The greatest product is: %d.", $greatestProduct);