Euler/euler14.php

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2015-11-19 19:43:31 +01:00
<?php
/*
* Gnieark's anwser to euler problem 14
* https://projecteuler.net/problem=14
*/
$longestSequence=0;
$startOfLongestSequence=0;
for($i=1;$i<1000000;$i++){
//echo $i."\n";
$long=countCollatzSequence($i);
if($long>$longestSequence){
$longestSequence=$long;
$startOfLongestSequence=$i;
}
}
echo $startOfLongestSequence;
function countCollatzSequence($start){
$count=1;
$number=$start;
$next=nextCollatzNumber($number);
while($number<>1){
$number=nextCollatzNumber($number);
$count++;
}
return $count;
}
function nextCollatzNumber($previous){
if(fmod($previous,2)==0){
//odd
return $previous/2;
}else{
//even
return 3 * $previous + 1;
}
}