PHP extract comparison operator - php

Question

I was asked on an interview what would be the fastest way to extract the comparison operator between two statements.
For example rate>=4 the comparison operator is '>=' it should be able to extract '>','<','!=','=','<=','>=','='
The function must return the comparison operator.
This is what I wrote, and they marked it as wrong.
function extractcomp($str)
{
$temp = [];
$matches = array('>','<','!','=');
foreach($matches as $match)
{
if(strpos($str,$match)!== false)
{
$temp[] = $match;
}
}
return implode('',$temp);
}
Does anyone have a better way?

Answer 1

you can read character by character once you hit the first occurrence you can determine what's gonna be the next character i.e.:
$ops = ['>','<','!','='];
$str = "rate!=4";
foreach($ops as $op)
{
if(($c1 = strpos($str, $op)) !== false)
{
$c2 = $str[$c1++] . (($str[$c1] == $ops[3]) ? $str[$c1] : "");
break;
}
}
echo $c2;
So if the first search character is ">" you can only assume the 2nd one is gonna be "=" or it doesn't exist. So you get the index of 1st character and increment it and check if the 2nd character exists in our search array or not. Then return the value. this will loop until it finds the 1st occurrence then breaks.
EDIT:
here's another solution:
$str = "rate!=4";
$arr = array_intersect(str_split($str), ['>','<','=','!']);
echo current($arr).(end($arr) ? end($arr) : '');
not as fast as the loop but definitely decreases the bloat code.
There's always a better way to optimize the code.

Answer 2

Unless they have some monkeywrenching strings to throw at this custom function, I recommend trim() with a ranged character mask. Something like echo trim('rate>=4',"A..Za..z0..9"); would work for your sample input in roughly half the time.
Code: (Demo)
function extractcomp($str){
return trim($str,"A..Za..z0..9");
}
echo extractcomp("rate>=4");
Regarding regex, better efficiency in terms of step count with preg_match() would be to use a character class to match the operators.
Assuming only valid operators will be used, you can use /[><!=]+/ or if you want to tighen up length /[><!=]{1,3}/
Just 8 steps on your sample input string. Demo
This is less strict than Andreas' | based pattern, but takes fewer steps.
It depends on how strict the pattern must be. My pattern will match !==.
If you want to improve your loop method, write a break after you have matched the entire comparison operator.
Actually, you are looping the operators. That would have been their issue (or one of them). Your method will not match ==. I'm not sure if that is a possible comparison (it is not in your list).