PHP code Issues with Out of Memory allocation

Question

There is a technique by which the list of (N+1) bit codes can be generated from (N)-bit codes.

Take the list of N bit codes in the given order and call it List-N
Reverse the above list (List-N), and name the new reflected list: Reflected-List-N
Prefix each member of the original list (List-N) with 0 and call this new list 'A'
Prefix each member of the new list (Reflected-List-N) with 1 and call this new list 'B'
The list of codes with N+1 bits is the concatenation of Lists A and B.

A Demonstration of the above steps: Generating the list of 3-bit Mystery Codes from 2-Bit Mystery Codes

2-bit list of codes: 00, 01, 11, 10
Reverse/Reflect the above list: 10, 11, 01, 00
Prefix Old Entries with 0: 000, 001, 011, 010
Prefix Reflected List with 1: 110, 111, 101, 100
Concatenate the lists obtained in the last two steps: 000, 001, 011, 010, 110, 111, 101, 100

But when I enter 65 as input getting error:

PHP Fatal error: Out of memory (allocated 538968064) in $result[]=$prefix.$value; line code

:: Code ::

<?php
function MysteryCodes($input){
    $initArr=array(0,1);

    $list=array();
    $list[0]=$initArr;
    for ($i=1; $i<$input; $i++)
    {
        $prevIndex=$i-1;
        $reflectedListN = array_reverse($list[$prevIndex]);
        $listA=prefixR($list[$prevIndex], '0');
        $listB=prefixR($reflectedListN, '1');
        $list[$i]=array_merge($listA, $listB);
    }
    return array_slice($list[$input-1], -$input);
}

function prefixR($input, $prefix){
    $result=array();
    foreach($input as $value){
        $result[]=$prefix.$value;
    }
    return $result;
}

$inp = 5;
if($inp>=1 && $inp<=65){
    $result=MysteryCodes($inp);
    $output="";
    foreach($result as $key=>$value)
        $output.="$value\n";

    echo $output;
}

Also is there any other way to overcome by changing code or logic for the same.

Thanks in advance.

Possible duplicate of PHP Strange issue with working code

Jirka Hrazdil
– Jirka Hrazdil

2017-12-21 14:00:20 +00:00
Commented Dec 21, 2017 at 14:00 — Jirka Hrazdil
– Jirka Hrazdil, Commented Dec 21, 2017 at 14:00

Jirka Hrazdil · Accepted Answer · 2017-12-21 10:48:51Z

0

For $inp = 65 your resulting array would contain 2^65 distinct binary values. You store each value as a string, which is not the most efficient way of storing binary digits. You could, probably, convert strings to integers for storing in an array and then back to string for calculations (reversing, prefixing) - but you would soon run into integer overflow - for values larger than 2^32 on 32-bit PHP and 2^64 on 64-bit PHP - see docs - values would then be converted to float type and you'll lose precision.

So you could be able to squeeze more values into the memory, but you'll definitely reach the point where regardless of what you do, the array just wouldn't fit into the memory_limit.

answered Dec 21, 2017 at 10:48

Jirka Hrazdil

4,0211 gold badge16 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

The Archer Over a year ago

Thanks for your replay. What you have said i understand but how can i resolved the issues? any hint will be appreciated.

Jirka Hrazdil Over a year ago

Apart from cramming more data into memory by using more efficient data storage structures you could also have the vast majority of the data in a file, and read into memory only small parts. This would, however, impose a huge speed penalty on the calculation.

Collectives™ on Stack Overflow

PHP code Issues with Out of Memory allocation

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related