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74 lines
3.2 KiB
PHP
74 lines
3.2 KiB
PHP
<?php
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/**
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* This function solves the problem 8 of the Project Euler.
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*
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* Problem description:
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*The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
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*73167176531330624919225119674426574742355349194934
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96983520312774506326239578318016984801869478851843
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85861560789112949495459501737958331952853208805511
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12540698747158523863050715693290963295227443043557
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66896648950445244523161731856403098711121722383113
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62229893423380308135336276614282806444486645238749
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30358907296290491560440772390713810515859307960866
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70172427121883998797908792274921901699720888093776
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65727333001053367881220235421809751254540594752243
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52584907711670556013604839586446706324415722155397
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53697817977846174064955149290862569321978468622482
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83972241375657056057490261407972968652414535100474
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82166370484403199890008895243450658541227588666881
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16427171479924442928230863465674813919123162824586
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17866458359124566529476545682848912883142607690042
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24219022671055626321111109370544217506941658960408
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07198403850962455444362981230987879927244284909188
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84580156166097919133875499200524063689912560717606
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05886116467109405077541002256983155200055935729725
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71636269561882670428252483600823257530420752963450
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*Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
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*/
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/**
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* @return int
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*/
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function problem8(): int
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{
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$theNumber = "73167176531330624919225119674426574742355349194934" .
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"96983520312774506326239578318016984801869478851843" .
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"85861560789112949495459501737958331952853208805511" .
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"12540698747158523863050715693290963295227443043557" .
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"66896648950445244523161731856403098711121722383113" .
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"62229893423380308135336276614282806444486645238749" .
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"30358907296290491560440772390713810515859307960866" .
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"70172427121883998797908792274921901699720888093776" .
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"65727333001053367881220235421809751254540594752243" .
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"52584907711670556013604839586446706324415722155397" .
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"53697817977846174064955149290862569321978468622482" .
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"83972241375657056057490261407972968652414535100474" .
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"82166370484403199890008895243450658541227588666881" .
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"16427171479924442928230863465674813919123162824586" .
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"17866458359124566529476545682848912883142607690042" .
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"24219022671055626321111109370544217506941658960408" .
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"07198403850962455444362981230987879927244284909188" .
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"84580156166097919133875499200524063689912560717606" .
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"05886116467109405077541002256983155200055935729725" .
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"71636269561882670428252483600823257530420752963450";
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$greatestProduct = 0;
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$substringSize = 13;
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for ($i = 0; $i < strlen($theNumber) - $substringSize; $i++) {
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$currentSubstring = substr($theNumber, $i, $substringSize);
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$currentProduct = 0;
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for ($j = 0; $j < strlen($currentSubstring); $j++) {
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$currentProduct = ($currentProduct == 0 ? (int)$currentSubstring[$j] : $currentProduct * (int)$currentSubstring[$j]);
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}
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$greatestProduct = ($greatestProduct < $currentProduct ? $currentProduct : $greatestProduct);
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}
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return $greatestProduct;
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}
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