array matching count one less than expected - php

Question

$ar is a sock of pairs. $n is the number of items in $ar. I have to match each number in the array with another if any of them match, its a pair. I have to then return the count of matched items. I have done it below but the answer is one less than what it should be. Example
n:9
ar: 10 20 20 10 10 30 50 10 20
I get output 2 instead of 3.
function sockMerchant($n, $ar) {
$pair =0;
$j=0;
for($i=0; $i< count($ar); $i++)
{
for($j=$i+1; $j< count($ar); $j++)
{
if ( isset( $ar[$j]) && isset( $ar[$i])) {
if ($ar[$i]== $ar[$j])
{
unset($ar[$i]);
unset($ar[$j]);
$pair+=1;
$i=0;
break;
}
}
}
}
return count($ar);
}

Answer 1

Instead of what you are doing there is shortcut to achieve the same,
$temp = array_count_values($arr); // count number of occurences
echo count(array_filter($temp, function($value){ // filter in not greater than 1
return $value > 1;
}));
The above snippet will give you all the pairs which are not only once.
Here is an one more alternative for your snippet,
$temp = array_count_values($arr); // count number of occurences
$e = array_reduce($temp, function ($carry, $item) {
$carry += ($item > 1 ? intval($item / 2) : 0);
return $carry;
});
echo $e;die;
Working demo.

Answer 2

$ar = [10, 20, 20, 10, 10, 30, 50, 10, 20];
$pairIndex = [];
$count = 0;
foreach ($ar as $key => $item) {
// Start comparing from the next element
for ($i = ($key + 1); $i < count($ar); $i++) {
if ($item == $ar[$i] && !in_array($key, $pairIndex)) {
$pairIndex[] = $key;
$pairIndex[] = $i;
$count++;
}
}
}
echo "Pairs: " . $count;

Answer 3

This will give you the number of pairs.
$arr = array(10, 20, 20, 10, 10, 30, 50, 10, 20);
$counts = array_count_values($arr); // count number of occurences
array_walk($counts, function(&$x) {$x = intdiv($x, 2);}); //divide each element
//by 2 (integer division), so now you have pairs of each element
echo array_sum($counts); //sum the pairs
Using your initial array, it echoes 3.

Answer 4

simple example what happens to your array:
$ar = array(0, 10, 20, 30, 40, 50 , 60, 70, 80, 90);
$lnPointer = 2;
print_r($ar);
// Array ( [0] => 0 [1] => 10 [2] => 20 [3] => 30 [4] => 40 [5] => 50 [6] => 60 [7] => 70 [8] => 80 [9] => 90 )
echo "<HR>";
echo $ar[$lnPointer];
echo "<HR>";
unset( $ar[$lnPointer]);
print_r($ar);
// Array ( [0] => 0 [1] => 10 [3] => 30 [4] => 40 [5] => 50 [6] => 60 [7] => 70 [8] => 80 [9] => 90 )
echo "<HR>";
echo $ar[$lnPointer];
after unsetting you get an undefined index

Answer 5

If you want total matched pair count then you should return $pair. But you are returning count($ar) which can not be correct in all the possible scenarios. Check the below code with output and new set of data:
<?php
function sockMerchant($n, $ar) {
$pair =0;
$j=0;
for($i=0; $i< $n; $i++)
{
for($j=$i+1; $j< $n; $j++)
{
if ( isset( $ar[$j]) && isset( $ar[$i])) {
if ($ar[$i]== $ar[$j])
{
unset($ar[$j]);
unset($ar[$i]);
$pair+=1;
$i=0;
break;
}
}
}
}
echo '<pre>'; print_r($ar);
return $pair.'--'.count($ar);
}
$a = [10, 20, 20, 10, 10, 30, 50, 10, 20, 80, 40];
$n = 11;
$b = sockMerchant($n, $a);
var_dump($b);
// Output:
/*
Array
(
[5] => 30
[6] => 50
[8] => 20
[9] => 80
[10] => 40
)
string(4) "3--5"
*/
?>
Demo