From 1eaf6eece16f10bdc7362541277f5ab08b27d780 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment?= <clement@desmidt.fr>
Date: Wed, 9 Dec 2020 13:06:05 +0100
Subject: [PATCH] :sparkles: Finit le jour 8

---
 day_8/part_1.php | 44 ++++++++++++++++++++++++++++++
 day_8/part_2.php | 71 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 day_8/part_1.php
 create mode 100644 day_8/part_2.php

diff --git a/day_8/part_1.php b/day_8/part_1.php
new file mode 100644
index 0000000..3604954
--- /dev/null
+++ b/day_8/part_1.php
@@ -0,0 +1,44 @@
+<?php
+
+$instructions = explode("\n", file_get_contents('input.txt'));
+
+$acc = 0;
+$used_indexes = [];
+$current_index = 0;
+
+while (true) {
+    if (in_array($current_index, $used_indexes, true)) {
+        echo $acc;
+        exit;
+    }
+    $used_indexes[] = $current_index;
+    $current_op = $instructions[$current_index];
+    [$command, $value] = explode(' ', $current_op);
+
+    if ($command === 'nop') {
+        $current_index++;
+        continue;
+    }
+
+    $math_op = $value[0];
+    $math_value = substr($value, 1);
+
+    if ($command === 'acc') {
+        if ($math_op === '+') {
+            $acc += (int)$math_value;
+        } else {
+            $acc -= (int)$math_value;
+        }
+        $current_index++;
+        continue;
+    }
+
+    if ($command === 'jmp') {
+        if ($math_op === '+') {
+            $current_index += (int)$math_value;
+        } else {
+            $current_index -= (int)$math_value;
+        }
+        continue;
+    }
+}
diff --git a/day_8/part_2.php b/day_8/part_2.php
new file mode 100644
index 0000000..37f940a
--- /dev/null
+++ b/day_8/part_2.php
@@ -0,0 +1,71 @@
+<?php
+
+$instructions = explode("\n", file_get_contents('input.txt'));
+
+$acc = 0;
+$used_indexes = [];
+$current_index = 0;
+$to_change = [];
+
+// find all nop and jmp indexes
+foreach ($instructions as $index => $instruction) {
+    if (in_array(substr($instruction, 0, 3), ['nop', 'jmp'])) {
+        $to_change[] = $index;
+    }
+}
+
+// copy instructions
+$original_instructions = $instructions;
+
+while (true) {
+    if (!array_key_exists($current_index, $instructions)) {
+        echo $acc;
+        exit;
+    }
+    if (in_array($current_index, $used_indexes, true)) {
+        // fail, reset and change next nop or jmp
+        $acc = 0;
+        $used_indexes = [];
+        $current_index = 0;
+        $instructions = $original_instructions;
+        $changed_instruction_index = array_shift($to_change);
+        $instruction_to_change = $instructions[$changed_instruction_index];
+        [$command, $math] = explode(' ', $instruction_to_change);
+        if ($command === 'nop') {
+            $instructions[$changed_instruction_index] = sprintf('jmp %s', $math);
+        } else {
+            $instructions[$changed_instruction_index] = sprintf('nop %s', $math);
+        }
+        continue;
+    }
+    $used_indexes[] = $current_index;
+    $current_op = $instructions[$current_index];
+    [$command, $value] = explode(' ', $current_op);
+
+    if ($command === 'nop') {
+        $current_index++;
+        continue;
+    }
+
+    $math_op = $value[0];
+    $math_value = substr($value, 1);
+
+    if ($command === 'acc') {
+        if ($math_op === '+') {
+            $acc += (int)$math_value;
+        } else {
+            $acc -= (int)$math_value;
+        }
+        $current_index++;
+        continue;
+    }
+
+    if ($command === 'jmp') {
+        if ($math_op === '+') {
+            $current_index += (int)$math_value;
+        } else {
+            $current_index -= (int)$math_value;
+        }
+        continue;
+    }
+}