From bd25a86f9eaa5680e74c283d9a7e135f9d0b0405 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20M=C3=A5rdbrink?= <hugo@mardbrink.se>
Date: Sun, 8 Dec 2024 18:11:50 +0100
Subject: [PATCH] Day 8

---
 d08/main.cxx | 171 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 165 insertions(+), 6 deletions(-)

diff --git a/d08/main.cxx b/d08/main.cxx
index 2b56230..24b3d8a 100644
--- a/d08/main.cxx
+++ b/d08/main.cxx
@@ -1,15 +1,174 @@
 #include <iostream>
-#include <fstream>
+#include <sstream>
+#include <string>
+#include <chrono>
+#include <vector>
+#include <unordered_map>
+#include <numeric>
+#include <unordered_set>
 
 using std::cout, std::endl;
 
-int main() {
-    std::ifstream file{"../d8/input.txt"};
+constexpr const char content[] = {
+    #embed "input.txt"
+};
+
+bool position_in_bounds(int x, int y, int max_x, int max_y) {
+    return x >= 0 && x <= max_x && y >= 0 && y <= max_y;
+}
+
+namespace std {
+    template <>
+    struct hash<std::pair<int, int>> {
+        std::size_t operator()(const std::pair<int, int>& p) const {
+            auto h1 = std::hash<int>{}(p.first);
+            auto h2 = std::hash<int>{}(p.second);
+            return h1 ^ (h2 << 1); 
+        }
+    };
+}
+
+void get_antinodes(std::unordered_set<std::pair<int, int>>& antinodes, std::pair<int, int> a1, std::pair<int, int> a2, int max_x, int max_y) { 
+    auto [x1, y1] = a1;
+    auto [x2, y2] = a2;
+    auto dx = x2 - x1; 
+    auto dy = y2 - y1;
+
+    auto gcd = std::gcd(dx, dy);
+    dx /= gcd;
+    dy /= gcd;
+
+    auto x_fst = x1 - dx;
+    auto y_fst = y1 - dy;
+    if(position_in_bounds(x_fst, y_fst, max_x, max_y)) {
+        antinodes.insert({x_fst, y_fst});
+    }
+
+    auto x_snd = x2 + dx;
+    auto y_snd = y2 + dy;
+    if(position_in_bounds(x_snd, y_snd, max_x, max_y)) {
+        antinodes.insert({x_snd, y_snd});
+    }
+}
+
+int part_1() {
+    std::istringstream input_stream(content);
+    std::string line;
+    std::unordered_map<char, std::vector<std::pair<int, int>>> frequencies_map;
+
+    auto row{0}, col{0};
+    while (std::getline(input_stream, line)) {
+        if(line.empty()) {
+            continue;
+        }
+        std::istringstream line_stream(line);
+        char frequency;
+        col = 0;
+        while (line_stream >> frequency) {
+            if(frequency != '.') {
+                if(frequencies_map.find(frequency) == frequencies_map.end()) {
+                    frequencies_map[frequency] = {};
+                }
+                frequencies_map[frequency].emplace_back(row, col);
+            }
+            col++;
+        }
+        row++;
+    } 
+    int max_x = row - 1, max_y = col - 1;
+
+    std::unordered_set<std::pair<int, int>> antinodes = {};
+    for(auto &[freq, positions] : frequencies_map) {
+        for(auto &pos_1 : positions) {
+            for(auto &pos_2 : positions) {
+                if(pos_1 != pos_2) {
+                    get_antinodes(antinodes, pos_1, pos_2, max_x, max_y);
+                }
+            }
+        }
+    }
+
+    return antinodes.size();
+}
+
+void get_all_antinodes(std::unordered_set<std::pair<int, int>>& antinodes, std::pair<int, int> a1, std::pair<int, int> a2, int max_x, int max_y) { 
+    int num_antinodes{0};
+
+    auto [x1, y1] = a1;
+    auto [x2, y2] = a2;
+    auto dx = x2 - x1; 
+    auto dy = y2 - y1;
+
+    auto gcd = std::gcd(dx, dy);
+    dx /= gcd;
+    dy /= gcd;
+
+    auto x_fst = x1 - dx;
+    auto y_fst = y1 - dy;
+    while(position_in_bounds(x_fst, y_fst, max_x, max_y)) {
+        antinodes.insert({x_fst, y_fst});
+        x_fst -= dx;
+        y_fst -= dy;
+    }
+
+    auto x_snd = x2 + dx;
+    auto y_snd = y2 + dy;
+    while(position_in_bounds(x_snd, y_snd, max_x, max_y)) {
+        antinodes.insert({x_snd, y_snd});
+        x_snd += dx;
+        y_snd += dy;
+    }
+}
+
+int part_2() {
+    std::istringstream input_stream(content);
     std::string line;
 
-    while (std::getline(file, line)) {
-        
+    std::unordered_map<char, std::vector<std::pair<int, int>>> frequencies_map;
+    std::unordered_set<std::pair<int, int>> antinodes = {};
+
+    auto row{0}, col{0};
+    while (std::getline(input_stream, line)) {
+        if(line.empty()) {
+            continue;
+        }
+        std::istringstream line_stream(line);
+        char frequency;
+        col = 0;
+        while (line_stream >> frequency) {
+            if(frequency != '.') {
+                if(frequencies_map.find(frequency) == frequencies_map.end()) {
+                    frequencies_map[frequency] = {};
+                }
+                frequencies_map[frequency].emplace_back(row, col);
+                antinodes.insert({row, col});
+            }
+            col++;
+        }
+        row++;
+    } 
+    int max_x = row - 1, max_y = col - 1;
+
+    for(auto &[freq, positions] : frequencies_map) {
+        for(auto &pos_1 : positions) {
+            for(auto &pos_2 : positions) {
+                if(pos_1 != pos_2) {
+                    get_all_antinodes(antinodes, pos_1, pos_2, max_x, max_y);
+                }
+            }
+        }
     }
-    
+
+    return antinodes.size();
+} 
+
+int main() {
+    std::chrono::steady_clock::time_point begin = std::chrono::steady_clock::now();
+    auto p1_val = part_1();
+    std::chrono::steady_clock::time_point middle = std::chrono::steady_clock::now();
+    auto p2_val = part_2();
+    std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
+    cout << "Part 1: " << p1_val << " (" << std::chrono::duration_cast<std::chrono::microseconds>(middle - begin).count() << "µs)" << endl;  
+    cout << "Part 2: " << p2_val << " (" << std::chrono::duration_cast<std::chrono::microseconds>(end - middle).count() << "µs)" << endl;
     return 0;
 }