PHP subtract the elements of an array within the elements - php

Question

I have an array [4,3,5,5,7,6] and I want to loop through the sorted one and subtract the highest value from the preceding value, then subtract the remainder from the value behind it and so on, then in the end, I need one final value that comes when the loop is completed.
For example
Above array will be sorted like
Array
(
[0] => 3
[1] => 4
[2] => 5
[3] => 5
[4] => 6
[5] => 7
)
Now I want to find the difference between arr[5] and arr[4], the result will be 1, then subtract the result from arr[3] and so on till the loop is completed
This is what I tried but it doesn't seem to work
for ($i = count($a)-1; $i >0; $i--){
echo $result = $a[$i] - $a[$i-1];
echo "<br />";
if($result > 0) {
if($result > $a[$i-2]) {
echo $result = $result - $a[$i-2];
} else {
}
}

Answer 1

I think there is a more simple and fast way to achieve this:
$array = [4, 3, 5, 5, 7, 6];
rsort($array);
$result = $array[0] - $array[1];
for($i = 2, $count = count($array); $i < $count; $i++){
$result = $array[$i] - $result;
}
print($result);
output:
0

Answer 2

Do you wish this way?
$a = [1,1,1,3,1,7];
$result = null;
for ($i = count($a)-1; $i >0; $i--){
if($result == null)
$result = $a[$i-1];
echo $result = $a[$i] - $result;
echo "<br />";
if($result == 0) break;
}

Answer 3

My first answer was wrong, i see you need to discard 2 keys after the first substraction.
This does the job:
<?php
$array = [3,4,5,5,6,7];
$reverse = array_reverse($array);
if (count($reverse) > 1) {
$first = $reverse[0] - $reverse[1];
} else {
//code should stop
}
$result = $first;
for ($i = 2; $i < count($reverse); $i++) {
$result = $reverse[$i] - $result;
}
echo $result;
Ouputs 0, just as in your example. And of course this code still needs check to see if the key of the array does exist while iterating

Answer 4

$numbers = [4,3,5,5,7,6];
sort($numbers);
$numbers = array_reverse($numbers);
$first = array_shift($numbers);
$second = array_shift($numbers);
$result = array_reduce($numbers, function ($carry, $current_item) {
return $current_item - $carry;
}, ($first - $second));
echo $result;

Answer 5

To get the expected output you are seeking you can use rsort to sort descending and start with the highest number. The first 2 elements are subtracted to get the starting value. Loop through the remainder to get your result.
Here's how you can achieve that:
$a = [4, 3, 5, 5, 7, 6]; // Your unsorted array
rsort($a); // Sort array by descending of largest to smallest
$result = $a[0] - $a[1]; // Initial subtraction of first two values
unset($a[0], $a[1]); // Remove from array so it won't loop through
foreach ($a as $_a) { // Loop through remainder and subtract difference
$result = $_a - $result;
}
echo $result; // Show your result
Yields:
0
If you care about reindexing due to the unset you can simply add an extra line after that:
$a = array_values($a); // Reindexes array starting at 0 if you desire