[2018-12-01] Add first challange samples and solution

Makefile

@@ -1,6 +1,8 @@
 .PHONY: day1 day2 day3 day4 day5 day6 day7 day8 day9 day10 day11 day12 day13 day14 day15 day16 day17 day18 day19 day20 day21 day22 day23 day24 day25
 
 day1:
+	php day1/main.php
+
 day2:
 day3:
 day4:

day1/main.php

@@ -0,0 +1,21 @@
+<?php
+// https://adventofcode.com/2018/day/1
+
+function puzzle1(array $changes) : int
+{
+    $frequency = 0;
+
+    foreach ($changes as $change) {
+        $frequency += $change;
+    }
+
+    return $frequency;
+}
+
+echo 'First challange samples:'.PHP_EOL;
+echo puzzle1(['+1','+1','+1']).PHP_EOL;              // 3
+echo puzzle1(['+1','+1','-2']).PHP_EOL;              // 0
+echo puzzle1(['-1','-2','-3']).PHP_EOL;              // -6
+
+echo 'First challange solution:'.PHP_EOL;
+echo puzzle1(explode(PHP_EOL, trim(file_get_contents(dirname(__FILE__).'/input.txt')))).PHP_EOL.PHP_EOL;