Add suggested solution

exercises/25/pacman_ai/solution/PacManAI.cpp

@@ -0,0 +1,33 @@
+GridPosition PacManAI::pelletClosestToPacman(GridPosition pacmanGridPosition,
+                                             std::vector<GridPosition> & pellets) {
+
+  auto pelletSort = [&pacmanGridPosition](GridPosition pelletA, GridPosition pelletB) {
+    double distanceA = positionDistance(pacmanGridPosition, pelletA);
+    double distanceB = positionDistance(pacmanGridPosition, pelletB);
+    return distanceA < distanceB;
+  };
+  std::sort(pellets.begin(), pellets.end(), pelletSort);
+  return pellets[0];
+}
+
+bool PacManAI::isValidMove(const Move & move) {
+  const bool isOpposite = (move.direction == oppositeDirection(direction));
+  if (isOpposite) {
+    return false;
+  }
+
+  const bool canWalk = isWalkableForPacMan(move.position);
+  if (!canWalk) {
+    return false;
+  }
+  return true;
+}
+
+Direction PacManAI::optimalDirection(const std::array<Move, 4> & moves) {
+  const auto optimalMove = std::min_element(moves.begin(), moves.end(), [](const auto & a, const auto & b) {
+    return a.distanceToTarget < b.distanceToTarget;
+  });
+
+  const auto & move = *optimalMove;
+  return move.direction;
+}