//Uses a depth first search to find any path that reaches the end goal
public static bool CheckPathExists(AIBoard board, bool isPlayerOne)
{
//Moves to be visited is used to prevent the revisiting of nodes by another branch.
HashSet <string> movesToBeVisited = new HashSet <string>();
Stack <SearchNode> spaces = new Stack <SearchNode>();
bool result = false;
//Adds the appropriate starting node depending on specified player.
if (isPlayerOne)
{
spaces.Push(new SearchNode(board.GetPlayerOnePos()));
}
else
{
spaces.Push(new SearchNode(board.GetPlayerTwoPos()));
}
while (spaces.Count != 0 && !result)
{
SearchNode currentNode = spaces.Pop();
//Check the win conditions of the appropriate player.
if (HasDirectPath(board, isPlayerOne, currentNode.space))
{
result = true;
break;
}
//Get the possible moves from the space of the current node.
List <string> movesFromSpace = board.GetAdjacentMoves(currentNode.space);
//Adds the appropriate nodes to the stack to be searched.
foreach (string move in movesFromSpace)
{
if (!movesToBeVisited.Contains(move))
{
spaces.Push(new SearchNode(move, currentNode.depth));
movesToBeVisited.Add(move);
}
}
}
return(result);
}
//Finds shortest path for the chosen player to the end of the board and returns it.
public static int FindShortestPath(AIBoard board, bool isPlayerOne)
{
Queue <SearchNode> spaces = new Queue <SearchNode>();
HashSet <string> movesToBeVisited = new HashSet <string>();
int result = -1;
if (isPlayerOne)
{
spaces.Enqueue(new SearchNode(board.GetPlayerOnePos()));
}
else
{
spaces.Enqueue(new SearchNode(board.GetPlayerTwoPos()));
}
movesToBeVisited.Add(spaces.Peek().space);
//Will exit after all paths return without finding end or
//break out of loop when first path to finish is found.
while (spaces.Count != 0 && result == -1)
{
SearchNode currentNode = spaces.Dequeue();
//Checks for easy direct path
if (HasDirectPath(board, isPlayerOne, currentNode.space))
{
result = currentNode.depth + FindDirectDistance(currentNode.space, isPlayerOne);
break;
}
//Get a list of moves from the current node location.
//If the node has not already been visited by this branch it is added to the queue.
List <string> movesFromSpace = board.GetAdjacentMoves(currentNode.space);
foreach (string move in movesFromSpace)
{
if (!movesToBeVisited.Contains(move))
{
spaces.Enqueue(new SearchNode(move, currentNode.depth));
movesToBeVisited.Add(move);
}
}
}
return(result);
}