Move solving logic to a separate class

solver/solver.cpp

@@ -0,0 +1,20 @@
+#include "solver.h"
+
+#include <sstream>
+
+Solver::Solver(std::string string) : puzzle_(Puzzle::FromString(string)) {}
+
+bool Solver::Solve() {
+  while (puzzle_.ApplyNextStep()) {
+  }
+  return puzzle_.IsSolved();
+}
+
+std::string Solver::State() { return puzzle_.CurrentState(); }
+
+std::string Solver::StateUrl() {
+  std::ostringstream stream;
+  stream << "https://tiramisu.one/sudoku.html?p=" << puzzle_.CurrentState()
+         << "&m=" << puzzle_.PencilMarkState();
+  return stream.str();
+}