From a299e1723f0a700a892720badab2e06a202d1eda Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Sun, 8 Dec 2024 07:49:46 +0100
Subject: Day 8 2024

---
 2024/08/day08a.cpp | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 2024/08/day08a.cpp

(limited to '2024/08/day08a.cpp')

diff --git a/2024/08/day08a.cpp b/2024/08/day08a.cpp
new file mode 100644
index 0000000..7a18ded
--- /dev/null
+++ b/2024/08/day08a.cpp
@@ -0,0 +1,49 @@
+#include <algorithm>
+#include <iostream>
+#include <map>
+#include <set>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
+using namespace std;
+
+pair<int, int> antinode(pair<int, int> p, pair<int, int> q) {
+	auto [xp, yp] = p;
+	auto [xq, yq] = q;
+	return make_pair(2*xp-xq, 2*yp-yq);
+}
+
+void add_antinodes(set<pair<int, int>>& points,
+    pair<int, int> p, set<pair<int, int>>& antinodes) {
+	for (auto q : points) {
+		antinodes.insert(antinode(p, q));
+		antinodes.insert(antinode(q, p));
+	}
+}
+
+int main() {
+	string line;
+	map<char, set<pair<int, int>>> d;
+	set<pair<int, int>> antinodes;
+	int i, j;
+	for (i = 0; getline(cin, line); i++) {
+		stringstream s(line);
+		char c;
+		for (j = 0; s >> c; j++) {
+			if (c != '.') {
+				pair<int, int> p(i, j);
+				add_antinodes(d[c], p, antinodes);
+				d[c].insert(p);
+			}
+		}
+	}
+	
+	int tot = 0;
+	for (auto [x, y] : antinodes)
+		if (x >= 0 && x < i && y >= 0 && y < j)
+			tot++;
+
+	cout << tot << endl;
+	return 0;
+}
-- 
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