<?php

$coordinates = array_map(static function ($line) {
    preg_match('/^(\d+),(\d+) -> (\d+),(\d+)$/', $line, $matches);
    array_shift($matches);
    return $matches;
}, explode("\n", file_get_contents('./input.txt')));

$grid = array_fill(0, 1000, array_fill(0, 1000, 0));

foreach ($coordinates as $coordinate) {
    if (is_horizontal($coordinate)) {
        $axis = $coordinate[0];
        $min = min($coordinate[1], $coordinate[3]);
        $max = max($coordinate[1], $coordinate[3]);
        for ($i = $min; $i <= $max; $i++) {
            $grid[$axis][$i]++;
        }
    } elseif (is_vertical($coordinate)) {
        $axis = $coordinate[1];
        $min = min($coordinate[0], $coordinate[2]);
        $max = max($coordinate[0], $coordinate[2]);
        for ($i = $min; $i <= $max; $i++) {
            $grid[$i][$axis]++;
        }
    }
}

$count = 0;
foreach ($grid as $row) {
    $count += count(array_filter($row, static function($cell) {
        return $cell >= 2;
    }));
}

echo $count;

function is_horizontal($coordinate)
{
    return $coordinate[0] === $coordinate[2];
}

function is_vertical($coordinate)
{
    return $coordinate[1] === $coordinate[3];
}