Day 8 2024

1 files changed, 49 insertions, 0 deletions

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;
+}