Minesweeper: make Field::flood_fill iterative

This change uses an iterative traversal to avoid stack overflows
in, the previously recursive, flood_fill.

Games/Minesweeper/Field.cpp

@@ -1,5 +1,6 @@
 #include "Field.h"
 #include <AK/HashTable.h>
+#include <AK/DoublyLinkedList.h>
 #include <LibCore/CConfigFile.h>
 #include <LibGUI/GButton.h>
 #include <LibGUI/GLabel.h>
@@ -271,15 +272,40 @@ void Field::reset()
  set_updates_enabled(true);
 }
 
+void Field::flood_mark(Square& square)
+{
+ if (square.is_swept)
+ return;
+ if (square.has_flag)
+ return;
+ if (square.is_considering)
+ return;
+ update();
+ square.is_swept = true;
+ square.button->set_visible(false);
+ square.label->set_visible(true);
+
+ --m_unswept_empties;
+
+ if (!m_unswept_empties)
+ win();
+}
+
 void Field::flood_fill(Square& square)
 {
- on_square_clicked(square);
- square.for_each_neighbor([this](auto& neighbor) {
- if (!neighbor.is_swept && !neighbor.has_mine && neighbor.number == 0)
- flood_fill(neighbor);
- if (!neighbor.has_mine && neighbor.number)
- on_square_clicked(neighbor);
- });
+ DoublyLinkedList<Square*> queue;
+ queue.append(&square);
+
+ for (auto s : queue) {
+ s->for_each_neighbor([this, &queue](Square& neighbor) {
+ if (!neighbor.is_swept && !neighbor.has_mine && neighbor.number == 0) {
+ flood_mark(neighbor);
+ queue.append(&neighbor);
+ }
+ if (!neighbor.has_mine && neighbor.number)
+ flood_mark(neighbor);
+ });
+ }
 }
 
 void Field::paint_event(GPaintEvent& event)

Games/Minesweeper/Field.h

@@ -67,6 +67,7 @@ class Field final : public GFrame {
  const Square& square(int row, int column) const { return *m_squares[row * columns() + column]; }
 
  void flood_fill(Square&);
+ void flood_mark(Square&);
 
  template<typename Callback>
  void for_each_square(Callback);