Get Products O(n)

main.php

<?php
$input = [-1,1,0,-3,3];

function getProducts(array $input) {
  // initialize output array with 1s
  $output = array_map(fn($el) => 1, $input);
  $length = count($input);

  // multiply each element by the elements before it
  $temp=1;
  for($ii=0; $ii<$length; $ii++) {
    $output[$ii] *= $temp;
    $temp *= $input[$ii];
  }

  // multiply each element by the elements after it
  $temp=1;
  for($ii=$length-1; $ii>=0; $ii--) {
    $output[$ii] *= $temp;
    $temp *= $input[$ii];
  }

  return $output;
}

print_r(getProducts($input));

This function computes the products of the members of the input array excluding the member at the current position. It multiplies each element by the elements that come before it, then it multiplies by the elements that come after it.

It has O(n) complexity.