From b6bd355be739f94206046b7247da9c387b786474 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sat, 7 Dec 2024 17:20:45 +0100
Subject: aoc 2024, day 7, part 2

---
 2024/src/day07.cpp | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

(limited to '2024')

diff --git a/2024/src/day07.cpp b/2024/src/day07.cpp
index 9b16b76..663e077 100644
--- a/2024/src/day07.cpp
+++ b/2024/src/day07.cpp
@@ -53,10 +53,69 @@ part1(const vector<tuple<long, vector<long>>>& data)
 	cout << sum << endl;
 }
 
+size_t
+ipow(size_t base, size_t exp) // NOLINT
+{
+	size_t result = 1;
+	while ( exp != 0 ) {
+		if ( (exp & 1U) == 1 ) {
+			result *= base;
+		}
+		exp >>= 1U;
+		base *= base;
+	}
+
+	return result;
+}
+
+bool
+can_evaluated2(long first, const vector<long>& values)
+{
+	const auto N = ipow(3, values.size() - 1); // NOLINT
+
+	for ( unsigned long pattern = 0; pattern != N; ++pattern ) {
+		auto test_pattern = pattern;
+
+		long result = values.at(0);
+		for ( size_t idx = 1; idx < values.size(); ++idx ) {
+			auto rem = test_pattern % 3;
+
+			if ( rem == 0 ) {
+				result += values.at(idx);
+			}
+			else if ( rem == 1 ) {
+				result *= values.at(idx);
+			}
+			else {
+				result = stol(to_string(result) + to_string(values.at(idx)));
+			}
+
+			test_pattern /= 3;
+		}
+		if ( first == result ) {
+			return true;
+		}
+	}
+	return false;
+}
+
+void
+part2(const vector<tuple<long, vector<long>>>& data)
+{
+	long sum = 0;
+	for ( const auto& [first, values]: data ) {
+		if ( can_evaluated2(first, values) ) {
+			sum += first;
+		}
+	}
+	cout << sum << endl;
+}
+
 int
 main()
 {
 	auto data = read_file("data/day07.txt");
 
 	part1(data);
+	part2(data);
 }
-- 
cgit v1.3