// Copy constructor. Sharing amphipod references doesn't matter.
public c_burrow(c_burrow other) : this(other.home_depth)
{
for (int column = 0; column < burrow_positions.Length; column++)
{
for (int row = 0; row < burrow_positions[column].Length; row++)
{
burrow_positions[column][row] = other.burrow_positions[column][row];
}
}
}
// Try to solve the burrow
public (bool, int) try_solve(bool pretty, List <c_burrow> solution_stack, string depth_string = "")
{
solution_stack.Add(new c_burrow(this));
if (pretty)
{
display("try_solve", depth_string);
}
int cost = 0;
// First try to move any amphipods to their solved positions. This is always the best thing to do.
int clear_cost = int.MaxValue;
while (clear_cost > 0)
{
clear_cost = 0;
clear_cost += try_clear_hallway();
clear_cost += try_clear_homes();
cost += clear_cost;
}
// if some amphipods were moved to their homes, note that in the solution stack.
if (cost > 0)
{
solution_stack.Add(new c_burrow(this));
if (pretty)
{
display(string.Format("moved some home (cost = {0})", cost), depth_string);
}
}
// If the burrow is solved, return.
if (is_solved())
{
if (pretty)
{
Console.WriteLine(depth_string + "solved!");
}
return(true, cost);
}
// I don't know what to do now but we have to move somebody out of a burrow.
// So try using brute force on every possible move and use the best result we find.
// ... turns out this still solves things in about a second. Yay!
List <c_burrow> best_guess_stack = null;
bool best_guess_solved = false;
int best_guess_cost = int.MaxValue;
// Loop through each home we could pull an amphipod out of
foreach (int start_column in k_home_columns)
{
(c_amphipod start, int start_row) = find_top_in_unfinished_home(start_column);
// If the top amphipod in this home was found
if (start != null)
{
(int min_end_column, int max_end_column) = get_valid_parking_spots(start_column);
// Loop through each place we could move it to
foreach (int end_column in k_hallway_parking_spot_columns)
{
if (end_column >= min_end_column && end_column <= max_end_column)
{
c_amphipod end = this.burrow_positions[end_column][0];
// If we find an empty spot to move it to
if (end == null)
{
// Move the amphipod to that spot in the hallway and recurse.
c_burrow guess = new c_burrow(this);
guess.burrow_positions[end_column][0] = start;
guess.burrow_positions[start_column][start_row] = null;
List <c_burrow> guess_stack = new List <c_burrow>();
(bool guess_solved, int guess_cost) = guess.try_solve(pretty, guess_stack, depth_string + "\t");
// If this branch of recursion solved the burrow and it's the best cost we've found so far, save the results.
if (guess_solved)
{
int initial_guess_cost = (start_row + Math.Abs(end_column - start_column)) * start.cost_per_move;
guess_cost += initial_guess_cost;
if (guess_cost < best_guess_cost)
{
best_guess_solved = true;
best_guess_cost = guess_cost;
best_guess_stack = guess_stack;
}
}
}
}
}
}
}
// Some branch of recursion found a solution.
if (best_guess_solved)
{
if (pretty)
{
Console.WriteLine(depth_string + "a guess solved");
}
solution_stack.AddRange(best_guess_stack);
return(best_guess_solved, cost + best_guess_cost);
}
// No solution was found.
else
{
if (pretty)
{
Console.WriteLine(depth_string + "no guesses solved");
}
return(false, 0);
}
}
