37 lines
700 B
PHP
37 lines
700 B
PHP
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<?php
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/*
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* Gnieark's anwser to euler problem 14
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* https://projecteuler.net/problem=14
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*/
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$longestSequence=0;
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$startOfLongestSequence=0;
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for($i=1;$i<1000000;$i++){
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//echo $i."\n";
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$long=countCollatzSequence($i);
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if($long>$longestSequence){
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$longestSequence=$long;
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$startOfLongestSequence=$i;
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}
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}
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echo $startOfLongestSequence;
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function countCollatzSequence($start){
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$count=1;
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$number=$start;
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$next=nextCollatzNumber($number);
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while($number<>1){
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$number=nextCollatzNumber($number);
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$count++;
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}
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return $count;
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}
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function nextCollatzNumber($previous){
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if(fmod($previous,2)==0){
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//odd
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return $previous/2;
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}else{
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//even
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return 3 * $previous + 1;
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}
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}
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