From 6f75463d197bf7802cca4059e404ed98b1c12062 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Thu, 14 Nov 2024 22:40:26 +0100
Subject: aoc 2015, day 11

---
 2015/src/day11.cpp | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 2015/src/day11.cpp

(limited to '2015/src/day11.cpp')

diff --git a/2015/src/day11.cpp b/2015/src/day11.cpp
new file mode 100644
index 0000000..06fd05b
--- /dev/null
+++ b/2015/src/day11.cpp
@@ -0,0 +1,66 @@
+#include <iostream>
+#include <regex>
+#include <string>
+
+using namespace std;
+
+void
+increment(string& str)
+{
+	for ( auto it = rbegin(str); it != rend(str); ++it ) {
+		*it += 1;
+		if ( *it > 'z' ) {
+			*it = 'a';
+			continue;
+		}
+		return;
+	}
+}
+
+bool
+has_increasing_chars(string_view str)
+{
+	for ( size_t idx = 2; idx != str.length(); ++idx ) {
+		if ( str[idx - 2] + 1 == str[idx - 1] && str[idx - 1] + 1 == str[idx] ) {
+			return true;
+		}
+	}
+	return false;
+}
+
+bool
+contains_no_invalid_char(const string& str)
+{
+	return str.find_first_of("iol") == string::npos;
+}
+
+bool
+contains_two_pairs(const string& str)
+{
+	static const regex regex("(.)\\1.*(.)\\2");
+
+	return regex_search(str, regex);
+}
+
+void
+part1(string& str)
+{
+	while ( true ) {
+		if ( has_increasing_chars(str) && contains_no_invalid_char(str) && contains_two_pairs(str) ) {
+			cout << str << endl;
+			break;
+		}
+		increment(str);
+	}
+}
+
+int
+main()
+{
+	string str = "hepxcrrq";
+
+	part1(str);
+
+	increment(str);
+	part1(str);
+}
-- 
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