aoc 2024, day 9, part 2

1 files changed, 88 insertions, 0 deletions

diff --git a/2024/src/day09.cpp b/2024/src/day09.cpp
index dd25a9d..7787c5c 100644
--- a/2024/src/day09.cpp
+++ b/2024/src/day09.cpp
@@ -1,7 +1,10 @@
 #include <fstream>
 #include <iostream>
 #include <iterator>
+#include <list>
+#include <ranges>
 #include <string>
+#include <vector>
 using namespace std;
 
 vector<int>
@@ -50,9 +53,94 @@ part1(const vector<int>& data)
         cout << sum << endl;
 }
 
+void
+part2(const vector<int>& data)
+{
+        // id, pos, len
+        vector<tuple<int, size_t, size_t>> files;
+
+        // pos, len
+        list<tuple<size_t, size_t>> spaces;
+
+        for ( size_t i = 0; i != data.size(); ) {
+                // skip space
+                auto j = i;
+                while ( j != data.size() && data.at(j) == -1 ) {
+                        ++j;
+                }
+                if ( i != j ) {
+                        spaces.emplace_back(i, j - i);
+                }
+                i = j;
+
+                while ( j != data.size() && data.at(i) == data.at(j) ) {
+                        ++j;
+                }
+                if ( i != j ) {
+                        files.emplace_back(data.at(i), i, j - i);
+                }
+                i = j;
+        }
+
+        for ( auto& file: std::ranges::reverse_view(files) ) {
+                for ( auto it = spaces.begin(); it != spaces.end(); ++it ) {
+                        if ( get<0>(*it) >= get<1>(file) ) {
+                                spaces.erase(it, spaces.end());
+                                break;
+                        }
+                        if ( get<1>(*it) >= get<2>(file) ) {
+                                // update pos
+                                get<1>(file) = get<0>(*it);
+
+                                // update space len
+                                get<1>(*it) -= get<2>(file);
+
+                                // update space pos
+                                get<0>(*it) += get<2>(file);
+
+                                if ( get<1>(*it) == 0 ) {
+                                        spaces.erase(it);
+                                }
+                                break;
+                        }
+                }
+        }
+
+        /*
+        for ( auto& file: std::ranges::reverse_view(files) ) {
+            auto space = ranges::find_if(spaces, [&](const auto& space) -> bool {
+                return get<1>(space) >= get<2>(file)  && get<0>(space) < get<1>(file);
+            });
+            if ( space != spaces.end() ) {
+                // update pos
+                get<1>(file) = get<0>(*space);
+
+                // update space len
+                get<1>(*space) -= get<2>(file);
+
+                // update space pos
+                get<0>(*space) += get<2>(file);
+
+                if ( get<1>(*space) == 0 ) {
+                    spaces.erase(space);
+                }
+            }
+        }
+        */
+
+        long sum = 0;
+        for ( const auto& [fid, pos, size]: files ) {
+                for ( size_t x = pos; x != pos + size; ++x ) {
+                        sum += long(x) * fid;
+                }
+        }
+        cout << sum << endl;
+}
+
 int
 main()
 {
         auto data = read_file("data/day09.txt");
         part1(data);
+        part2(data);
 }