aoc 2024, day 7, optimized solution

1 files changed, 112 insertions, 0 deletions

diff --git a/2024/src/day07-opti.cpp b/2024/src/day07-opti.cpp
new file mode 100644
index 0000000..7700b63
--- /dev/null
+++ b/2024/src/day07-opti.cpp
@@ -0,0 +1,112 @@
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+using namespace std;
+
+vector<tuple<long, vector<long>>>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+
+        vector<tuple<long, vector<long>>> data;
+        for ( string line; getline(input, line); ) {
+                auto pos = line.find(':');
+
+                stringstream str{ line.substr(pos + 1) };
+                data.emplace_back(stol(line.substr(0, pos)), vector<long>{ istream_iterator<long>{ str }, {} });
+        }
+        return data;
+}
+
+void
+part1(const vector<tuple<long, vector<long>>>& data)
+{
+        auto can_evaluated = [](long first, vector<long> values) -> bool {
+                set<long> candidates = { first };
+
+                while ( values.size() > 1 ) {
+                        auto value = values.back();
+                        values.pop_back();
+
+                        set<long> new_candidates;
+                        for ( const auto candidate: candidates ) {
+                                if ( candidate % value == 0 ) {
+                                        new_candidates.insert(candidate / value);
+                                }
+                                if ( candidate >= value ) {
+                                        new_candidates.insert(candidate - value);
+                                }
+                        }
+
+                        candidates = new_candidates;
+                }
+
+                return values.size() == 1 && candidates.contains(values.back());
+        };
+
+        long sum = 0;
+        for ( const auto& [first, values]: data ) {
+                if ( can_evaluated(first, values) ) {
+                        sum += first;
+                }
+        }
+        cout << sum << endl;
+}
+
+void
+part2(const vector<tuple<long, vector<long>>>& data)
+{
+        auto can_evaluated = [](long first, vector<long> values) -> bool {
+                set<long> candidates = { first };
+
+                while ( values.size() > 1 ) {
+                        auto value = values.back();
+                        values.pop_back();
+
+                        set<long> new_candidates;
+                        for ( const auto candidate: candidates ) {
+                                if ( candidate % value == 0 ) {
+                                        new_candidates.insert(candidate / value);
+                                }
+                                if ( candidate >= value ) {
+                                        new_candidates.insert(candidate - value);
+                                }
+
+                                if ( candidate > value ) {
+                                        auto value_str     = to_string(value);
+                                        auto candidate_str = to_string(candidate);
+
+                                        if ( candidate_str.ends_with(value_str) ) {
+                                                candidate_str.erase(candidate_str.length() - value_str.length());
+                                                new_candidates.insert(stol(candidate_str));
+                                        }
+                                }
+                        }
+
+                        candidates = new_candidates;
+                }
+
+                return values.size() == 1 && candidates.contains(values.back());
+        };
+
+        long sum = 0;
+        for ( const auto& [first, values]: data ) {
+                if ( can_evaluated(first, values) ) {
+                        sum += first;
+                }
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        auto data = read_file("data/day07.txt");
+
+        part1(data);
+        part2(data);
+}