<?php

declare(strict_types=1);

\$input = <<<\'PHP\'
190: 10 19
3267: 81 40 27
83: 17 5
156: 15 6
7290: 6 8 6 15
161011: 16 10 13
192: 17 8 14
21037: 9 7 18 13
292: 11 6 16 20
PHP;

return array_sum(array_map(
    static fn (Equation \$equation): int => \$equation->testValue,
    array_filter(
        array_map(
            static fn (string \$notation): Equation => Equation::create(\$notation),
            explode(\"\\n\", \$input),
        ),
        static fn (Equation \$equation): bool => \$equation->valid(),
    ),
));

final readonly class Equation
\{
    /**
     * @param int[] \$numbers
     */
    public function __construct(
        public int \$testValue,
        public array \$numbers,
    ) \{\}

    public function valid(bool \$part2 = true): bool
    \{
        return \$this->process(\$this->numbers, \$part2);
    \}

    public static function create(string \$input): self
    \{
        preg_match_all(\'/\\d+/\', \$input, \$matches);

        \$numbers = array_map(\'intval\', \$matches[0]);
        \$testValue = array_shift(\$numbers);

        return new self(\$testValue, \$numbers);
    \}

    private function process(array \$numbers, bool \$part2): bool
    \{
        if (\\count(\$numbers) === 1) \{
            return \$numbers[0] === \$this->testValue;
        \}

        \$left = array_shift(\$numbers);
        \$right = array_shift(\$numbers);

        if (\$left > \$this->testValue) \{
            return false;
        \}

        return \$this->process([\$left * \$right, ...\$numbers], \$part2)
            || \$this->process([\$left + \$right, ...\$numbers], \$part2)
            || (\$part2 && \$this->process([(int) \"\{\$left\}\{\$right\}\", ...\$numbers], true));
    \}
\}