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152 lines
5.2 KiB
PHP
152 lines
5.2 KiB
PHP
<?php
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/*
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* This function solves the problem 11 of the Project Euler.
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*
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* Problem description:
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* In the 20×20 grid below, four numbers along a diagonal line have been marked in red.
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08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
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49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
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81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
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52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
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22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
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24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
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32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
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67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
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24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
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21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
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78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
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16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
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86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
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19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
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04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
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88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
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04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
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20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
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20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
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01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48
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The product of these numbers is 26 × 63 × 78 × 14 = 1788696.
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What is the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid?
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Solution: 70600674
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*/
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function horizontalProduct($grid, $row, $col)
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{
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$product = 1;
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for ($i = 0; $i < 4; $i++) {
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$product *= $grid[$row][$col + $i];
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}
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return $product;
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}
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function verticalProduct($grid, $row, $col)
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{
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$product = 1;
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for ($i = 0; $i < 4; $i++) {
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$product *= $grid[$row + $i][$col];
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}
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return $product;
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}
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function diagonalRightProduct($grid, $row, $col)
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{
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$product = 1;
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for ($i = 0; $i < 4; $i++) {
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$product *= $grid[$row + $i][$col + $i];
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}
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return $product;
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}
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function diagonalLeftProduct($grid, $row, $col)
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{
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$product = 1;
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for ($i = 0; $i < 4; $i++) {
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$product *= $grid[$row + $i][$col - $i];
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}
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return $product;
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}
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function problem11()
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{
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$grid = "08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
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49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
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81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
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52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
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22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
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24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
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32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
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67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
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24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
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21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
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78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
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16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
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86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
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19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
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04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
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88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
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04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
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20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
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20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
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01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48";
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//Transform the grid string to a matrix data type (nested arrays)
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$grid = explode(' ', $grid);
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$grid_matrix = [];
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$row = [];
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$i = 0;
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$matrix_size = 20;
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//Convert string $grid to a matrix
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foreach ($grid as $g) {
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$i++;
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$row[] = (int)trim($g);
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if ($i == $matrix_size) {
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$grid_matrix[] = $row;
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$row = [];
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$i = 0;
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}
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}
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$maxProduct = 0;
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for ($row = 0; $row < $matrix_size; $row++) {
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for ($col = 0; $col < $matrix_size; $col++) {
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// horizontal
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if ($col < $matrix_size - 3) {
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$product = horizontalProduct($grid_matrix, $row, $col);
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if ($product > $maxProduct) {
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$maxProduct = $product;
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}
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}
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// vertical
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if ($row < $matrix_size - 3) {
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$product = verticalProduct($grid_matrix, $row, $col);
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if ($product > $maxProduct) {
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$maxProduct = $product;
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}
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}
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// diagonal right
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if ($col < $matrix_size - 3 && $row < $matrix_size - 3) {
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$product = diagonalRightProduct($grid_matrix, $row, $col);
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if ($product > $maxProduct) {
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$maxProduct = $product;
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}
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}
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// diagonal left
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if ($col > 2 && $row < $matrix_size - 3) {
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$product = diagonalLeftProduct($grid_matrix, $row, $col);
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if ($product > $maxProduct) {
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$maxProduct = $product;
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}
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}
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}
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}
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return $maxProduct;
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}
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