Day 8 2024

5 files changed, 144 insertions, 0 deletions

diff --git a/2024/08/Makefile b/2024/08/Makefile
new file mode 100644
index 0000000..d335110
--- /dev/null
+++ b/2024/08/Makefile
@@ -0,0 +1,24 @@
+CC=g++ -std=c++20 -g -Wall
+
+a:
+        ${CC} -o a.out day08a.cpp
+
+b:
+        ${CC} -o b.out day08b.cpp
+
+clean:
+        rm -f a b
+
+atest: a
+        ./a.out
+
+btest: b
+        ./b.out
+
+arun: a
+        ./a.out < input
+
+brun: b
+        ./b.out < input
+
+.PHONY: a b clean atest btest arun brun
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;
+}
diff --git a/2024/08/day08b.cpp b/2024/08/day08b.cpp
new file mode 100644
index 0000000..1d1381f
--- /dev/null
+++ b/2024/08/day08b.cpp
@@ -0,0 +1,68 @@
+#include <algorithm>
+#include <iostream>
+#include <map>
+#include <set>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
+using namespace std;
+
+#define N 50
+#define M 50
+
+bool in_range(int x, int y) {
+        return x >= 0 && x < N && y >= 0 && y < M;
+}
+
+vector<pair<int, int>> antinode_all(pair<int, int> p, pair<int, int> q) {
+        auto [xp, yp] = p;
+        auto [xq, yq] = q;
+        /* In theory these two coefficients must be divided by the gcd of
+         * of the coordinates, which leads to possibly more points,
+         * as far as I understood the problem statement. Apparently, this
+         * is not the case. */
+        int gx = (xp - xq);
+        int gy = (yp - yq);
+        vector<pair<int, int>> v;
+        for (int i = 0; in_range(xp+i*gx, yp+i*gy); i++)
+                v.push_back(make_pair(xp+i*gx, yp+i*gy));
+        for (int i = 0; in_range(xq-i*gx, yq-i*gy); i++)
+                v.push_back(make_pair(xq-i*gx, yq-i*gy));
+        return v;
+}
+
+void add_antinodes(set<pair<int, int>>& points,
+    pair<int, int> p, set<pair<int, int>>& antinodes) {
+        for (auto q : points) {
+                auto a = antinode_all(p, q);
+                for (auto r : a)
+                        antinodes.insert(r);
+        }
+}
+
+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 (in_range(x, y))
+                        tot++;
+
+        cout << tot << endl;
+        return 0;
+}
diff --git a/2024/learned.txt b/2024/learned.txt
index 3a01fc0..86d32ff 100644
--- a/2024/learned.txt
+++ b/2024/learned.txt
@@ -6,3 +6,4 @@ List of things I learned (or refreshed) with this year's AoC.
 * Day 4: nothing special, some practice with classic and a weird trick
   to assign two variables at once with a pair of references pair<int&, int&>
 * Day 5: std::find and std::replace
+* Day 8: set::insert_range(), but it is from C++23 only
diff --git a/2024/template.cpp b/2024/template.cpp
index 7508a23..b2fd4ec 100644
--- a/2024/template.cpp
+++ b/2024/template.cpp
@@ -1,5 +1,7 @@
 #include <algorithm>
 #include <iostream>
+#include <map>
+#include <set>
 #include <sstream>
 #include <string>
 #include <string_view>