Add part one of day 3

src/Day3.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace AdventOfCode21;
+
+class Day3 extends AbstractCommand
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected static int $day = 3;
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part1(array $data): int
+    {
+        $bits = [];
+
+        foreach ($data as $binary) {
+            $split = str_split($binary);
+
+            foreach ($split as $position => $value) {
+                $bits[$position][] = $value;
+            }
+        }
+
+        $gammaRate = '';
+        $epsilonRate = '';
+
+        foreach ($bits as $values) {
+            $zeros = array_filter($values, static fn ($value) => $value === '0');
+            $ones = array_filter($values, static fn ($value) => $value === '1');
+
+            $gammaRate .= ($ones > $zeros) ? '1' : '0';
+            $epsilonRate .= ($ones < $zeros) ? '1' : '0';
+        }
+
+        return (int) (bindec($gammaRate) * bindec($epsilonRate));
+    }
+
+    /**
+     * @param string[] $data
+     * @param int      $position
+     * @param bool     $highest
+     *
+     * @return string
+     *
+     * @psalm-return '0'|'1'
+     */
+    private function valueAtPosition(array $data, int $position, bool $highest = true): string
+    {
+        $zeros = count(array_filter($data, static fn ($value) => $value[$position] === '0'));
+        $ones = count(array_filter($data, static fn ($value) => $value[$position] === '1'));
+
+        if ($highest) {
+            return $zeros > $ones ? '0' : '1';
+        }
+
+        if ($zeros === $ones) {
+            return '0';
+        }
+
+        // If there are more zeros, return 1 (as that is the lowest).
+        return $zeros > $ones ? '1' : '0';
+    }
+}