aoc 2024, day5

1 files changed, 104 insertions, 0 deletions

diff --git a/2024/src/day05.cpp b/2024/src/day05.cpp
new file mode 100644
index 0000000..37d74c6
--- /dev/null
+++ b/2024/src/day05.cpp
@@ -0,0 +1,104 @@
+#include <fstream>
+#include <iostream>
+#include <numeric>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<long>
+split(const string& line, char sep = ',')
+{
+        vector<long> parts;
+        stringstream input{ line };
+
+        for ( string part; getline(input, part, sep); ) {
+                parts.emplace_back(stol(part));
+        }
+
+        return parts;
+}
+
+tuple<vector<tuple<long, long>>, vector<vector<long>>>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+
+        vector<tuple<long, long>> rules;
+        for ( string line; getline(input, line); ) {
+                if ( line.empty() ) {
+                        break;
+                }
+                long lhs = 0;
+                long rhs = 0;
+                sscanf(line.c_str(), "%ld|%ld", &lhs, &rhs); // NOLINT
+                rules.emplace_back(lhs, rhs);
+        }
+
+        vector<vector<long>> pages;
+        for ( string line; getline(input, line); ) {
+                pages.emplace_back(split(line));
+        }
+        return { rules, pages };
+}
+
+bool
+is_valid(const vector<tuple<long, long>>& rules, const vector<long>& page)
+{
+        set<long> processed;
+
+        bool invalid = false;
+        for ( const auto& num: page ) {
+                processed.emplace(num);
+
+                auto pred = [num](const tuple<long, long>& rule) {
+                        return get<0>(rule) == num;
+                };
+
+                for ( auto it = find_if(rules.begin(), rules.end(), pred); it != rules.end(); it = find_if(it + 1, rules.end(), pred) ) {
+                        const auto foo = get<1>(*it);
+
+                        if ( processed.contains(foo) ) {
+                                invalid = true;
+                        }
+                }
+        }
+        return !invalid;
+}
+
+void
+part1(const vector<tuple<long, long>>& rules, const vector<vector<long>>& pages)
+{
+        long sum = 0;
+        for ( const auto& page: pages ) {
+                if ( is_valid(rules, page) ) {
+                        sum += page.at(page.size() / 2);
+                }
+        }
+        cout << sum << endl;
+}
+
+void
+part2(const vector<tuple<long, long>>& rules, const vector<vector<long>>& pages)
+{
+        long sum = 0;
+        for ( auto page: pages ) {
+                if ( !is_valid(rules, page) ) {
+                        ranges::sort(page, [&](auto lhs, auto rhs) -> bool {
+                                return ranges::find(rules, make_tuple(lhs, rhs)) != rules.end();
+                        });
+
+                        sum += page.at(page.size() / 2);
+                }
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        auto [rules, pages] = read_file("data/day05.txt");
+        part1(rules, pages);
+        part2(rules, pages);
+}