Solution for day 1.

2015/day1.php

@@ -1,3 +1,63 @@
 <?php
 
-// enter the solution for day 1 here.
+// Problem: https://adventofcode.com/2015/day/1
+
+/*
+ * Solution 1
+ *
+ * Runtime: ~0.158ms
+ */
+function solution1() {
+  $start_time = microtime(true);
+  $instructions = file_get_contents('./inputs/day1.txt');
+  $up_floors = substr_count($instructions, "(");
+  $down_floors = substr_count($instructions, ")");
+  $total = $up_floors - $down_floors;
+  echo "The answer is $total\n";
+  $end_time = microtime(true);
+  $execution_time = ($end_time - $start_time);
+  echo $execution_time * 1000 . "\n";
+}
+solution1();
+
+/*
+ * Solution 2
+ *
+ * Runtime: ~0.622ms
+ */
+function solution2() {
+  $start_time = microtime(true);
+  $instructions = file_get_contents('./inputs/day1.txt');
+  $chars = str_split($instructions);
+  $floor = 0;
+  foreach ($chars as $char) {
+    match ($char) {
+      "(" => $floor++,
+      ")" => $floor--,
+      default => 0,
+    };
+  }
+  echo "The answer is $floor\n";
+  $end_time = microtime(true);
+  $execution_time = ($end_time - $start_time);
+  echo $execution_time * 1000 . "\n";
+}
+solution2();
+
+/*
+ * Solution 3
+ *
+ * Runtime: ~0
+ */
+function solution3() {
+  $start_time = microtime(true);
+  $instructions = file_get_contents('./inputs/day1.txt');
+  $chars = str_split($instructions);
+  $values = array_count_values($chars);
+  $floor = $values['('] - $values[')'];
+  echo "The answer is $floor\n";
+  $end_time = microtime(true);
+  $execution_time = ($end_time - $start_time);
+  echo $execution_time * 1000 . "\n";
+}
+solution3();