From 637e029dc17e542854f9104c381c6ef6bdf5d137 Mon Sep 17 00:00:00 2001
From: Clement Desmidt <clement@desmidt.fr>
Date: Mon, 13 Dec 2021 11:14:13 +0100
Subject: [PATCH] :sparkles: Finit le jour 12

---
 day_12/part_1.php | 45 +++++++++++++++++++++++++++++++++++++++++++++
 day_12/part_2.php | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 day_12/part_1.php
 create mode 100644 day_12/part_2.php

diff --git a/day_12/part_1.php b/day_12/part_1.php
new file mode 100644
index 0000000..48bf190
--- /dev/null
+++ b/day_12/part_1.php
@@ -0,0 +1,45 @@
+<?php
+
+$paths = explode("\n", file_get_contents('./input.txt'));
+
+$possible_paths = [];
+
+foreach ($paths as $path) {
+    [$start, $end] = explode('-', $path);
+
+    if ($start !== 'end' && $end !== 'start') {
+        if (array_key_exists($start, $possible_paths)) {
+            $possible_paths[$start][] = $end;
+        } else {
+            $possible_paths[$start] = [$end];
+        }
+    }
+
+    if ($start !== 'start' && $end !== 'end') {
+        if (array_key_exists($end, $possible_paths)) {
+            $possible_paths[$end][] = $start;
+        } else {
+            $possible_paths[$end] = [$start];
+        }
+    }
+}
+
+echo track($possible_paths, 'start', []);
+
+function track($possible_paths, $cave, $history)
+{
+    $count = 0;
+    $history[] = $cave;
+    foreach ($possible_paths[$cave] as $path) {
+        if ($path === 'end') {
+            $count++;
+        } elseif (ctype_lower($path) && in_array($path, $history)) {
+            continue;
+        } else {
+            $count += track($possible_paths, $path, $history);
+        }
+    }
+
+    return $count;
+}
+
diff --git a/day_12/part_2.php b/day_12/part_2.php
new file mode 100644
index 0000000..25eb1d6
--- /dev/null
+++ b/day_12/part_2.php
@@ -0,0 +1,44 @@
+<?php
+
+$paths = explode("\n", file_get_contents('./input.txt'));
+
+$possible_paths = [];
+
+foreach ($paths as $path) {
+    [$start, $end] = explode('-', $path);
+
+    if ($start !== 'end' && $end !== 'start') {
+        if (array_key_exists($start, $possible_paths)) {
+            $possible_paths[$start][] = $end;
+        } else {
+            $possible_paths[$start] = [$end];
+        }
+    }
+
+    if ($start !== 'start' && $end !== 'end') {
+        if (array_key_exists($end, $possible_paths)) {
+            $possible_paths[$end][] = $start;
+        } else {
+            $possible_paths[$end] = [$start];
+        }
+    }
+}
+
+echo track($possible_paths, 'start', [], false);
+
+function track($possible_paths, $cave, $history, $went_once) {
+    $count = 0;
+    $history[] = $cave;
+    foreach ($possible_paths[$cave] as $path) {
+        if ($path === 'end') {
+            $count++;
+        } elseif(ctype_lower($path) && in_array($path,$history)) {
+            if ($went_once === false) {
+                $count += track($possible_paths, $path, $history, true);
+            }
+        } else {
+            $count += track($possible_paths, $path, $history, $went_once);
+        }
+    }
+    return $count;
+}