re: AoC Day 6: Chronal Coordinates VIEW POST

FULL DISCUSSION
 

PHP solution

Part 1 took me a while to figure out how to get rid of coordinates that have infinite area. Part 2 was straight forward loop.

Btw using array_filter was ~3x slower than foreach loop. PHP ¯\(ツ)

Part 1

<?php
$array = require_once 'readFile.php';

function calcDist($p1, $p2, $q1, $q2) {
  return abs($p1 - $q1) + abs($p2 - $q2);
}

$top = INF;
$right = 0;
$bottom = 0;
$left = INF;

foreach ($array as $value) {
  $top = (int)min($value[1], $top);
  $right = (int)max($value[0], $right);
  $bottom = (int)max($value[1], $bottom);
  $left = (int)min($value[0], $left);
}

$distances = [];
for ($i=$top; $i <= $bottom; $i++) {
  for ($j=$left; $j <= $right; $j++) {
    $index;
    $minDist = INF;
    $isUnique = true;
    foreach ($array as $key => $value) {
      $dist = calcDist($i, $j, $value[1], $value[0]);

      if ($dist == 0) {
        $index = $key;
      } else if ($dist == $minDist) {
        $isUnique = false;
        $index = '.';
      } else if ($dist < $minDist) {
        $isUnique = true;
        $minDist = $dist;
        $index = $key;
      }
    }

    $distances[$i][$j] = $index;
  }
}

function getEdges($array) {
  $firstRow = array_shift($array);
  $lastRow = array_pop($array);

  $edges = array_filter(array_merge($firstRow, $lastRow), function($val) {
    return $val != '.';
  });

  foreach ($array as $cols) {
    $first = array_shift($cols);
    $last = array_pop($cols);

    $first != '.' && $edges[] = $first;
    $last != '.' && $edges[] = $last;
  }
  return array_unique($edges);
}

$edges = getEdges($distances);

$max = 0;
$len = count($array);
for ($i=0; $i < $len; $i++) {
  if (in_array($i, $edges)) {
    continue;
  }

  $res = 0;

  foreach ($distances as $cols) {
    foreach ($cols as $val) {
      if ($val != '.' && $i == $val) {
        $res++;
      }
    }
  }

  if ($res > $max) {
    $max = $res;
  }
}

echo $max;
?>

Part2

<?php
$array = require_once 'readFile.php';

define("TOTAL_DIST", 10000);

function calcDist($p, $q) {
  return abs($p[0] - $q[0]) + abs($p[1] - $q[1]);
}

$top = INF;
$right = 0;
$bottom = 0;
$left = INF;

foreach ($array as $value) {
  $top = (int)min($value[1], $top);
  $right = (int)max($value[0], $right);
  $bottom = (int)max($value[1], $bottom);
  $left = (int)min($value[0], $left);
}

$distances = 0;

for ($i=$top; $i <= $bottom; $i++) {
  for ($j=$left; $j <= $right; $j++) {
    $dist = 0;
    foreach ($array as $key => $value) {
      $dist += calcDist([$i, $j], [(int)$value[1], (int)$value[0]]);
    }
    if ($dist < TOTAL_DIST) {
      $distances++;
    }
  }
}

echo $distances;
?>

readFile.php

<?php
$file = fopen("input.txt", "r") or exit("Unable to open file");

while(!feof($file)) {
  $array[] = explode(", ", fgets($file));
}

fclose($file);

return array_filter(array_map(function($val) {
  return array((int)$val[0], (int)$val[1]);
}, $array));
?>
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