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| 1 | +<?php |
| 2 | + |
| 3 | +namespace Failedcode\Aoc2022\Days; |
| 4 | + |
| 5 | +class Day9 extends AbstractDay |
| 6 | +{ |
| 7 | + public function solve_part_1(): string |
| 8 | + { |
| 9 | + $moves = $this->getMoves(); |
| 10 | + $headX = $headY = 0; |
| 11 | + $tailX = $tailY = 0; |
| 12 | + $tailPositions = []; |
| 13 | + foreach ($moves as $move) { |
| 14 | + list($x, $y) = $move; |
| 15 | + $tailPositions["{$tailX}|{$tailY}"] = true; |
| 16 | + $headX += $x; |
| 17 | + $headY += $y; |
| 18 | + |
| 19 | + if (!$this->inRange($headX, $headY, $tailX, $tailY)) { |
| 20 | + $xdiff = $headX - $tailX; |
| 21 | + $ydiff = $headY - $tailY; |
| 22 | + if ($headX != $tailX && $headY != $tailY) { |
| 23 | + // diagonal |
| 24 | + $tailX += $this->sign($xdiff); |
| 25 | + $tailY += $this->sign($ydiff); |
| 26 | + } elseif (abs($xdiff) > abs($ydiff)) { |
| 27 | + $tailX += $this->sign($xdiff); |
| 28 | + } elseif (abs($ydiff) > abs($xdiff)) { |
| 29 | + $tailY += $this->sign($ydiff); |
| 30 | + } |
| 31 | + $tailPositions["{$tailX}|{$tailY}"] = true; |
| 32 | + } |
| 33 | + } |
| 34 | + |
| 35 | + return count($tailPositions); |
| 36 | + } |
| 37 | + |
| 38 | + public function solve_part_2(): string |
| 39 | + { |
| 40 | + return "TODO"; |
| 41 | + } |
| 42 | + |
| 43 | + protected function sign($n) |
| 44 | + { |
| 45 | + if ($n > 0) { |
| 46 | + return 1; |
| 47 | + } |
| 48 | + if ($n < 0) { |
| 49 | + return -1; |
| 50 | + } |
| 51 | + return 0; |
| 52 | + } |
| 53 | + |
| 54 | + protected function inRange($x1, $y1, $x2, $y2) |
| 55 | + { |
| 56 | + return abs($x1 - $x2) < 2 && abs($y1 - $y2) < 2; |
| 57 | + } |
| 58 | + |
| 59 | + protected function getMoves() |
| 60 | + { |
| 61 | + $moves = []; |
| 62 | + $inputList = $this->util->loadInput(9); |
| 63 | + foreach ($inputList as $row) { |
| 64 | + if (empty($row)) { |
| 65 | + continue; |
| 66 | + } |
| 67 | + list($dir, $n) = explode(' ', trim($row), 2); |
| 68 | + for ($i = 0; $i < (int)$n; $i += 1) { |
| 69 | + switch ($dir) { |
| 70 | + case 'R': $moves[] = [1, 0]; break; |
| 71 | + case 'L': $moves[] = [-1, 0]; break; |
| 72 | + case 'D': $moves[] = [0, 1]; break; |
| 73 | + case 'U': $moves[] = [0, -1]; break; |
| 74 | + } |
| 75 | + } |
| 76 | + } |
| 77 | + return $moves; |
| 78 | + } |
| 79 | +} |
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