From 8f53e809e312021596be70317ea053e5bec6c816 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Mon, 6 Jan 2025 13:58:31 +0100
Subject: aoc 2015, day 25

---
 2015/src/day25.cpp | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 2015/src/day25.cpp

(limited to '2015/src')

diff --git a/2015/src/day25.cpp b/2015/src/day25.cpp
new file mode 100644
index 0000000..ed02c9b
--- /dev/null
+++ b/2015/src/day25.cpp
@@ -0,0 +1,53 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <vector>
+using namespace std;
+
+tuple<long, long>
+read_file(string_view filename)
+{
+	fstream input{ filename };
+
+	vector<long> values;
+	for ( string word; input >> word; ) {
+		long value{};
+		if ( stringstream(word) >> value ) {
+			values.push_back(value);
+		}
+	}
+	return { values.at(0), values.at(1) };
+}
+
+long
+triangle_num(long row, long col)
+{
+	const auto side = row + col - 1;
+	return (side * (side + 1)) / 2 - row;
+}
+
+long
+powmod(long base, long pow, long mod)
+{
+	long result = 0;
+	for ( result = 1; pow != 0; pow /= 2 ) {
+		if ( pow % 2 == 1 ) {
+			result = (result * base) % mod;
+		}
+		base = (base * base) % mod;
+	}
+	return result;
+}
+
+void
+part1(long row, long col)
+{
+	cout << (powmod(252533, triangle_num(row, col), 33554393) * 20151125) % 33554393 << endl;
+}
+
+int
+main()
+{
+	const auto [row, col] = read_file("data/day25.txt");
+	part1(row, col);
+}
-- 
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