Pairs of opposite values [closed] - php

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I need to write a function that when i have an array with n numbers from -10 to 10 (without 0) returns quantity of pairs from the array which sum gives 0.
For example:
$input = array (3, 6, -3, 5, -10, 3, 10, 1, 7, -1, -9, -8, 7, 7, -7, -2, -7);
In example right answer is 5 (pairs are bolded)
i figure out something like that:
<?php
$array = [3, 6, -3, 5, -10, 3, 10, 1, 7, -1, -9, -8, 7, 7, -7, -2, -7];
function pairs($array=[]){
$copy = $array;
$arrayLength = count($copy);
$pairs=0;
while($arrayLength!=0){
$a = array_values($array)[0];
$b = -$a;
for( $i=1 ; $i==$arrayLength ; $i++ ){
if($array[$i]==$b){
unset($array[$i]);
$pairs++;
$arrayLength--;
}
else{
unset($array[$i]);
$arrayLength--;
}
}
return $pairs;
}
unset($copy);
}
var_dump(pairs($array));
?>

Answer 1

Try out this one:
function pairs($array=[]){
$pairs = [];
// counting the positive and negative of each number in the set
foreach($array as $v){
$av = abs($v);
if(!isset($pairs[$av]))
$pairs[$av] = [
'pos' => 0,
'neg' => 0
];
($v > 0) ? $pairs[$av]['pos']++ : $pairs[$av]['neg']++;
}
$pair_count = 0;
// getting the number of pairs for each number, based on those counts
foreach($pairs as $pair){
$pair_count += min($pair['pos'],$pair['neg']);
}
return $pair_count;
}
DEMO
This gets rid of the annoying need to rebuild the array indexes every time you unset (part of where your issues with your provided function are coming from), and also makes it so you only need to loop through it twice and therefore is more efficient, especially for large data sets.