1 files changed, 65 insertions, 8 deletions

diff --git a/src/day12.cpp b/src/day12.cpp
index b01b2fb..11bd80b 100644
--- a/src/day12.cpp
+++ b/src/day12.cpp
@@ -1,5 +1,6 @@
 #include <fstream>
 #include <iostream>
+#include <map>
 #include <sstream>
 #include <string>
 #include <vector>
@@ -69,9 +70,9 @@ count_groups(string_view str)
 }
 
 long
-brute_force(string_view puzzle, const vector<long>& nums)
+brute_force(string_view springs, const vector<long>& groups)
 {
-        long counts = count_if(puzzle.begin(), puzzle.end(), [](char chr) { return chr == '?'; });
+        long counts = count_if(springs.begin(), springs.end(), [](char chr) { return chr == '?'; });
 
         string test_pattern;
 
@@ -79,7 +80,7 @@ brute_force(string_view puzzle, const vector<long>& nums)
         for ( size_t counter = 0; counter != (1U << size_t(counts)); ++counter ) {
                 auto bit_pattern = counter;
 
-                for ( char chr: puzzle ) {
+                for ( char chr: springs ) {
                         if ( chr == '?' ) {
                                 if ( (bit_pattern & 1U) != 0U ) {
                                         test_pattern += '.';
@@ -93,7 +94,7 @@ brute_force(string_view puzzle, const vector<long>& nums)
                                 test_pattern += chr;
                         }
                 }
-                if ( nums == count_groups(test_pattern) ) {
+                if ( groups == count_groups(test_pattern) ) {
                         arrangements++;
                 }
 
@@ -103,16 +104,71 @@ brute_force(string_view puzzle, const vector<long>& nums)
         return arrangements;
 }
 
+long
+count(const string& springs, const vector<long>& groups)
+{
+        map<tuple<string, vector<long>>, long> cache;
+
+        function<long(string, const vector<long>&)> count_rec = [&](string springs, const vector<long>& groups) -> long {
+                auto cached_value = cache.find(make_tuple(springs, groups));
+                if ( cached_value != cache.end() ) {
+                        return cached_value->second;
+                }
+
+                springs.erase(0, springs.find_first_not_of('.'));
+
+                if ( springs.empty() ) {
+                        return groups.empty() ? 1 : 0;
+                }
+
+                if ( groups.empty() ) {
+                        return springs.find('#') == string_view::npos ? 1 : 0;
+                }
+
+                if ( springs[0] == '#' ) {
+                        auto gidx = size_t(groups[0]);
+                        if ( springs.length() < gidx || springs.substr(0, gidx).find('.') != string_view::npos || springs[gidx] == '#' ) {
+                                return 0;
+                        }
+
+                        return count_rec(springs.substr(gidx + 1), { groups.begin() + 1, groups.end() });
+                }
+
+                auto value = count_rec(string("#") + springs.substr(1), groups) + count_rec(springs.substr(1), groups);
+
+                cache[make_tuple(springs, groups)] = value;
+
+                return value;
+        };
+
+        return count_rec(springs + ".", groups);
+}
+
 void
 part1(const vector<string>& input)
 {
         auto sum = 0L;
         for ( const auto& line: input ) {
-                auto parts  = split(line, ' ');
-                auto puzzle = parts[0];
-                auto nums   = read_ints(parts[1]);
+                auto parts   = split(line, ' ');
+                auto springs = parts[0];
+                auto groups  = read_ints(parts[1]);
+
+                sum += brute_force(springs, groups);
+                // sum += count(springs, groups);
+        }
+        cout << sum << endl;
+}
+
+void
+part2(const vector<string>& input)
+{
+        auto sum = 0L;
+        for ( const auto& line: input ) {
+                auto parts   = split(line, ' ');
+                auto springs = parts[0] + "?" + parts[0] + "?" + parts[0] + "?" + parts[0] + "?" + parts[0];
+                auto groups  = read_ints(parts[1] + "," + parts[1] + "," + parts[1] + "," + parts[1] + "," + parts[1]);
 
-                sum += brute_force(puzzle, nums);
+                sum += count(springs, groups);
         }
         cout << sum << endl;
 }
@@ -122,4 +178,5 @@ main()
 {
         const auto input = read_file("data/day12.txt");
         part1(input);
+        part2(input);
 }