1 files changed, 42 insertions, 0 deletions

diff --git a/src/day24.cpp b/src/day24.cpp
index 296d38a..76f459b 100644
--- a/src/day24.cpp
+++ b/src/day24.cpp
@@ -2,9 +2,12 @@
 #include <fstream>
 #include <iostream>
 #include <limits>
+#include <map>
 #include <string>
 #include <tuple>
 #include <vector>
+#include <z3++.h>
+
 using namespace std;
 
 using line_type   = tuple<double, double, double, double, double, double>;
@@ -122,10 +125,49 @@ part1(const puzzle_type& input)
         cout << sum << endl;
 }
 
+void
+part2(const puzzle_type& input)
+{
+        auto config  = z3::config();
+        auto context = z3::context(config);
+        auto solver  = z3::solver(context);
+
+        const auto px = context.int_const("px");
+        const auto py = context.int_const("py");
+        const auto pz = context.int_const("pz");
+        const auto vx = context.int_const("vx");
+        const auto vy = context.int_const("vy");
+        const auto vz = context.int_const("vz");
+
+        for ( size_t i = 0; i != input.size(); ++i ) {
+                const auto& stone = input[i];
+
+                const auto pxn = context.int_val(int64_t(get<0>(stone)));
+                const auto pyn = context.int_val(int64_t(get<1>(stone)));
+                const auto pzn = context.int_val(int64_t(get<2>(stone)));
+                const auto vxn = context.int_val(int64_t(get<3>(stone)));
+                const auto vyn = context.int_val(int64_t(get<4>(stone)));
+                const auto vzn = context.int_val(int64_t(get<5>(stone)));
+                const auto tn  = context.int_const(to_string(i+1).c_str());
+
+                solver.add(tn >= 0);
+                solver.add(pxn + vxn * tn == px + vx * tn);
+                solver.add(pyn + vyn * tn == py + vy * tn);
+                solver.add(pzn + vzn * tn == pz + vz * tn);
+        }
+
+        solver.check();
+
+        auto model = solver.get_model();
+
+        cout << model.eval(px).as_int64() + model.eval(py).as_int64() + model.eval(pz).as_int64() << endl;
+}
+
 int
 main()
 {
         const auto input = read_file("data/day24.txt");
 
         part1(input);
+        part2(input);
 }