Implement day 06.

I forgot how slow std::regex was to compile.

2019/src/day06.cpp

@@ -1,23 +1,81 @@
 #include <iostream>
 #include <regex>
+#include <queue>
+#include <unordered_set>
 #include "days.hpp"
 
-void aoc2019::day06_part1(std::istream &input, std::ostream &output) {
-    std::string buffer;
-    std::regex regex("^([A-Z0-9]+)\\)([A-Z0-9]+)$");
+namespace {
+    std::vector<std::pair<std::string, std::string>> read_orbits(std::istream &input) {
+        std::vector<std::pair<std::string, std::string>> result;
+        std::string buffer;
 
-    while (std::getline(input, buffer)) {
+        std::regex regex("^([A-Z0-9]+)\\)([A-Z0-9]+)$");
         std::smatch match_results;
 
-        if (!std::regex_match(buffer, match_results, regex)) {
-            std::string error = "Invalid line: ";
-            error += buffer;
-            throw std::domain_error(error);
+        while (std::getline(input, buffer)) {
+            if (!std::regex_match(buffer, match_results, regex)) {
+                std::string error = "Invalid line: ";
+                error += buffer;
+                throw std::domain_error(error);
+            }
+
+            result.emplace_back(match_results[1], match_results[2]);
+        }
+
+        return result;
+    }
+}
+
+void aoc2019::day06_part1(std::istream &input, std::ostream &output) {
+    std::unordered_map<std::string, std::vector<std::string>> orbits;
+
+    for (auto[a, b] : read_orbits(input)) {
+        orbits[std::move(a)].emplace_back(std::move(b));
+    }
+
+    std::deque<std::pair<std::string, int>> todo = {{"COM", 0}};
+    int total_orbits = 0;
+
+    while (!todo.empty()) {
+        auto[name, offset] = todo.front();
+        todo.pop_front();
+
+        total_orbits += offset;
+
+        for (const auto& partner : orbits[name]) {
+            todo.emplace_back(partner, offset + 1);
         }
     }
-	output << "Not implemented\n";
+
+    output << total_orbits << std::endl;
 }
 
 void aoc2019::day06_part2(std::istream &input, std::ostream &output) {
-	output << "Not implemented\n";
+    std::unordered_map<std::string, std::vector<std::string>> orbits;
+
+    for (auto[a, b] : read_orbits(input)) {
+        orbits[a].emplace_back(b);
+        orbits[b].emplace_back(a);
+    }
+
+    std::deque<std::pair<std::string, int>> todo = {{"YOU", 0}};
+    std::unordered_set<std::string> visited = { "YOU" };
+
+    while (!todo.empty()) {
+        auto[name, offset] = todo.front();
+        todo.pop_front();
+
+        for (const auto& partner : orbits[name]) {
+            if (partner == "SAN") {
+                output << offset - 1 << std::endl;
+                return;
+            }
+            if (!visited.count(partner)) {
+                todo.emplace_back(partner, offset + 1);
+                visited.emplace(partner);
+            }
+        }
+    }
+
+    throw std::domain_error("No valid path.");
 }

2019/tests/samples/06-2-1.in

@@ -0,0 +1,13 @@
+COM)B
+B)C
+C)D
+D)E
+E)F
+B)G
+G)H
+D)I
+E)J
+J)K
+K)L
+K)YOU
+I)SAN

2019/tests/samples/06-2-1.out

@@ -0,0 +1 @@
+4