tree conversions

test.php

<?php


function makeLeafs($list)
{
    $result = [];
    if (is_string($list)) {
        return [$list => null];
    }

    foreach ($list as $key => $value) {
        if (is_int($key)) {
            $result[$value] = null;
            continue;
        }

        $result[$key] = makeLeafs($value);

    }
    return $result;
}

$input = ['foo'];

var_dump(makeLeafs($input));

$input = ['foo', 'bar'];

var_dump(makeLeafs($input));

$input = ['foo' => 'bar'];

var_dump(makeLeafs($input));

$input = ['foo' => ['bar', 'buz']];

var_dump(makeLeafs($input));

$input = ['foo' => ['bar' => 'buz']];

var_dump(makeLeafs($input));