✨ Finit le jour 3

day_3/part_1.php

@@ -0,0 +1,16 @@
+<?php
+
+$lines = array_map('str_split', explode("\n", file_get_contents('input.txt')));
+$lines = array_map('array_reverse', array_map(null, ...$lines)); // matrix rotation
+
+$gamma = '';
+$epsilon = '';
+
+foreach ($lines as $line) {
+    $counts = array_count_values($line);
+    $max = array_search(max($counts), $counts);
+    $gamma .= $max;
+    $epsilon .= $max === 1 ? 0 : 1;
+}
+
+echo bindec($gamma) * bindec($epsilon);

day_3/part_2.php

@@ -0,0 +1,52 @@
+<?php
+
+$lines = array_map('str_split', explode("\n", file_get_contents('input.txt')));
+
+$oxygen_lines = $lines;
+for ($i = 0, $l = count($oxygen_lines[0]); $i < $l; $i++) {
+    if (count($oxygen_lines) <= 1) {
+        break;
+    }
+    $rotated_lines = array_map('array_reverse', array_map(null, ...$oxygen_lines)); // matrix rotation
+    $max = determine_max_number_at_line($rotated_lines, $i);
+    $oxygen_lines = array_filter($oxygen_lines, static function ($line) use ($max, $i) {
+        return $line[$i] == $max;
+    });
+}
+
+$co2_lines = $lines;
+for ($i = 0, $l = count($co2_lines[0]); $i < $l; $i++) {
+    if (count($co2_lines) <= 1) {
+        break;
+    }
+    $rotated_lines = array_map('array_reverse', array_map(null, ...$co2_lines)); // matrix rotation
+    $min = determine_min_number_at_line($rotated_lines, $i);
+    $co2_lines = array_filter($co2_lines, static function ($line) use ($min, $i) {
+        return $line[$i] == $min;
+    });
+}
+
+$oxygen = implode(current($oxygen_lines));
+$co2 = implode(current($co2_lines));
+
+echo bindec($oxygen) * bindec($co2);
+
+function determine_max_number_at_line($rotated_lines, $line_number): bool|int|string
+{
+    $line = $rotated_lines[$line_number];
+    $counts = array_count_values($line);
+    if ($counts[0] === $counts[1]) {
+        return 1;
+    }
+    return array_search(max($counts), $counts);
+}
+
+function determine_min_number_at_line($rotated_lines, $line_number): bool|int|string
+{
+    $line = $rotated_lines[$line_number];
+    $counts = array_count_values($line);
+    if ($counts[0] === $counts[1]) {
+        return 0;
+    }
+    return array_search(min($counts), $counts);
+}