20 lines
425 B
PHP
20 lines
425 B
PHP
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<?php
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/*
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* Gnieark's anwser to euler problem 21
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* https://projecteuler.net/problem=21
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*/
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include("_functions.php");
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$sumOfDivisors=array();
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for($i=1;$i<10000;$i++){
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$sumOfDivisors[$i]=array_sum(getAllDivisors($i,true,false));
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}
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$sum=0;
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//If d(a) = b and d(b) = a, where a ≠ b,
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foreach($sumOfDivisors as $a => $d){
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if((isset($sumOfDivisors[$d])) && ($sumOfDivisors[$d]==$a) && ($a<>$d)){
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$sum+=$a;
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}
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}
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echo $sum;
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