From 22d5bd5e7a8b0340bdcafa3d65a1ad3669d1a33d Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Mon, 9 Dec 2024 17:35:26 +0100
Subject: aoc 2024, day 9, part 1

---
 2024/src/day09.cpp | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 2024/src/day09.cpp

(limited to '2024/src')

diff --git a/2024/src/day09.cpp b/2024/src/day09.cpp
new file mode 100644
index 0000000..dd25a9d
--- /dev/null
+++ b/2024/src/day09.cpp
@@ -0,0 +1,58 @@
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <string>
+using namespace std;
+
+vector<int>
+read_file(string_view filename)
+{
+	fstream input{ filename };
+	string  line;
+	int     fid = 0;
+
+	getline(input, line);
+
+	vector<int> data;
+	for ( size_t i = 0; i != line.size(); ++i ) {
+		vector<int> values(size_t(line.at(i) - '0'), (i % 2 == 0) ? fid++ : -1);
+		data.insert(data.end(), values.begin(), values.end());
+	}
+	return data;
+}
+
+void
+part1(const vector<int>& data)
+{
+	vector<int> result;
+
+	auto lhs = data.begin();
+	auto rhs = data.end();
+
+	while ( lhs != rhs ) {
+		if ( *lhs != -1 ) {
+			result.push_back(*lhs);
+		}
+		else {
+			--rhs;
+			while ( *rhs == -1 ) {
+				--rhs;
+			}
+			result.push_back(*rhs);
+		}
+		++lhs;
+	}
+
+	long sum = 0;
+	for ( size_t i = 0; i != result.size(); ++i ) {
+		sum += long(i) * result.at(i);
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	auto data = read_file("data/day09.txt");
+	part1(data);
+}
-- 
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