I have this block of code.
$input = 4;
$list_N = array('0', '1');
for($n=1; $n<=$input; $n++) {
if($n%2 == 0) {
$c++;
}
$reverse_list_N = array_reverse($list_N);
$A = array();
$B = array();
for($i=0; $i<count($list_N); $i++) {
$A[] = '0' . $list_N[$i];
$B[] = '1' . $reverse_list_N[$i];
}
$list_N = array_merge($A[], $B[]);
if($n == 1) {
$list_N = array('0', '1');
}
}
$array_sliced = array_slice($list_N, -1*$input, $input);
for($i=0; $i<count($array_sliced); $i++) {
$output = implode("\n", $array_sliced);
}
echo "<pre>"; print_r($output); echo "</pre>";
What this code does is, it generates following data (starting from (0,1)):
0,1
00, 01, 11, 10
000, 001, 011, 010, 110, 111, 101, 100
....... and so on
When $input = 4; the output is:
1010
1011
1001
1000
And as you can see, after every loop the the elements in the $list_N array doubles than the previous one. And with this pace if $input = 25; then the array would have 33554432 elements which is very huge. And that is the problem I couldn't find a solution of. When $input = 60 I get this error
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 36 bytes)
on this line
$list_N = array_merge($A, $B);
Even setting the memory limit to 2G did not solve it. So, how do I optimize my code in order to same the memory. Or, is there any other solution ?
Update: Following steps are used to generate the data.
$list_N is an array
$reverse_list is the reverse of $list_N
0 is appended in the beginning of every element in the $list_N array and stored in $A
1 is appended in the beginning of every element in the $reverse_list_N array and stored in $B
Array $A and array $B are merged and is stored in $list_N.
The main loop runs for $input number of times and the last $input number of elements are displayed from the final array.
Solution:
Try using an SplFixedArray!
About:
A SplFixedArrayis
about 37% of a regular "array" of the same size
and
The
SplFixedArrayclass provides the main functionalities of array. The advantage is that it allows a faster array implementation.
From: Documentation Page
Example:
$startMemory = memory_get_usage();
$array = new SplFixedArray(100000);
for ($i = 0; $i < 100000; ++$i) {
$array[$i] = $i;
}
echo memory_get_usage() - $startMemory, ' bytes';
Further Reading:
Read more: http://nikic.github.io/2011/12/12/How-big-are-PHP-arrays-really-Hint-BIG.html
Messier Solution:
Another solution that could help, which I don't recommend is to override the default memory capacity. You can do this using this:
ini_set('memory_limit', '-1')
Further Reading:
@tadman was right. This requires a different approach. I ran the numbers, the array size at input 65 assuming just 1 byte per array element is 32 Exabytes (insane amount of memory required just to run this script).
//we assume user will enter input as a valid positive integer > 1
fscanf(STDIN, "%d\n", $target);
$base=["0","1"];
$root=["0","1"];
$newArr=$base;
for($i=1;$i<7;$i++)//pre-initialize root array
$newArr=genNextArray($newArr);
//echo "-----------\n";
//print_r($root);
//we're ready to display the output now based on the root array elements
displayNBits($target);
function displayNBits($target)
{
global $root;
$arr=array();
for($i=0;$i<$target;$i++)
{
$elem=str_pad($root[$i],$target,"0",STR_PAD_LEFT);
$elem[0]="1";
$arr[]=$elem;
}
$arr=array_reverse($arr);
for($i=0;$i<count($arr);$i++)
echo $arr[$i]."\n";
//print_r($arr);
}
function genNextArray($arr)
{
global $root;
$newArr= array(count($arr)*2);
$ni=0;
//0 prefix (left to right sweep)
for($i=0;$i<count($arr);$i++)
{
$newArr[$ni]="0".$arr[$i];
$ni++;
}
//1 prefix (right to left sweep)
for($i=count($arr)-1;$i>=0;$i--)
{
$newArr[$ni]="1".$arr[$i];
$root[]=$newArr[$ni];
$ni++;
}
return $newArr;
}