aoc 2024, day 7, part 2

1 files changed, 59 insertions, 0 deletions

diff --git a/2024/src/day07.cpp b/2024/src/day07.cpp
index 9b16b76..663e077 100644
--- a/2024/src/day07.cpp
+++ b/2024/src/day07.cpp
@@ -53,10 +53,69 @@ part1(const vector<tuple<long, vector<long>>>& data)
         cout << sum << endl;
 }
 
+size_t
+ipow(size_t base, size_t exp) // NOLINT
+{
+        size_t result = 1;
+        while ( exp != 0 ) {
+                if ( (exp & 1U) == 1 ) {
+                        result *= base;
+                }
+                exp >>= 1U;
+                base *= base;
+        }
+
+        return result;
+}
+
+bool
+can_evaluated2(long first, const vector<long>& values)
+{
+        const auto N = ipow(3, values.size() - 1); // NOLINT
+
+        for ( unsigned long pattern = 0; pattern != N; ++pattern ) {
+                auto test_pattern = pattern;
+
+                long result = values.at(0);
+                for ( size_t idx = 1; idx < values.size(); ++idx ) {
+                        auto rem = test_pattern % 3;
+
+                        if ( rem == 0 ) {
+                                result += values.at(idx);
+                        }
+                        else if ( rem == 1 ) {
+                                result *= values.at(idx);
+                        }
+                        else {
+                                result = stol(to_string(result) + to_string(values.at(idx)));
+                        }
+
+                        test_pattern /= 3;
+                }
+                if ( first == result ) {
+                        return true;
+                }
+        }
+        return false;
+}
+
+void
+part2(const vector<tuple<long, vector<long>>>& data)
+{
+        long sum = 0;
+        for ( const auto& [first, values]: data ) {
+                if ( can_evaluated2(first, values) ) {
+                        sum += first;
+                }
+        }
+        cout << sum << endl;
+}
+
 int
 main()
 {
         auto data = read_file("data/day07.txt");
 
         part1(data);
+        part2(data);
 }