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<?php
const EL_COUNT = 7;
function permute($what)
{
if (count($what) == 1) {
return [$what];
}
$options = [];
foreach($what as $el) {
$seen = 0;
array_push($options, ...array_map(
fn ($arr) => [$el, ...$arr],
permute(
array_filter(
$what,
fn ($subel)
=> $subel != $el || $seen++
)
)
));
}
return $options;
}
function four_squares($input)
{
$results = [];
if (count($input) != EL_COUNT) {
return $results;
}
foreach (permute($input) as $case) {
$real_case = [0, ...$case, 0];
$summed_groups = array_map(
fn ($el)
=> array_sum(
array_map(
fn ($subel)
=> $real_case[$subel],
range($el, $el + 2))
),
array_filter(
array_keys($real_case),
fn ($el)
=> $el % 2 == 0 && $el <= count($real_case) - 2
)
);
$matching_first = array_filter(
$summed_groups,
fn ($el)
=> $el == $summed_groups[0]
);
if (count($matching_first) == count($summed_groups)) {
$case_results = [];
for ($letter = 'a'; $letter != 'h'; ++$letter) {
$case_results[$letter] = array_shift($case);
}
$results[] = $case_results;
}
}
return $results;
}
var_dump(four_squares(range(1, 7)));
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