✨ Pathfinding with Dijkstra

funcs/games/hex.py

@@ -16,6 +16,12 @@ AIScoresHex = {
 }
 
 BOARDWIDTH = 11
+ALL_POSITIONS = [(i,j) for i in range(11) for j in range(11)]
+ALL_SET = set(ALL_POSITIONS)
+EMPTY_DIJKSTRA = {}
+for position in ALL_POSITIONS:
+    EMPTY_DIJKSTRA[position] = math.inf # an impossibly high number
+HEX_DIRECTIONS = [(0,1),(-1,1),(-1,0),(0,-1),(1,-1),(1,0)]
 
 
 # Parses command
@@ -200,14 +206,48 @@ def placeOnHexBoard(board,player,position):
         logThis("Cannot place on existing piece (error code 1532)")
         return "Error. You must place on an empty space."
 
-# Checks if someone has won the game and returns the winner
-def isHexWon(board):
-    won = 0
-    winningPieces = []
 
-    # you know... code here
+def evaluateBoard(board):
+    score = {1:0, 2:0}
+    isWon = False
+    # Here, I use Dijkstra's algorithm to evaluate the board, as proposed by this article: https://towardsdatascience.com/hex-creating-intelligent-adversaries-part-2-heuristics-dijkstras-algorithm-597e4dcacf93
+    for player in [1,2]:
+        logThis("Running Dijkstra for player "+str(player))
+        Distance = copy.deepcopy(EMPTY_DIJKSTRA)
+        # Initialize the starting hexes. For the blue player, this is the leftmost column. For the red player, this is the tom row. 
+        for start in (ALL_POSITIONS[::11] if player == 2 else ALL_POSITIONS[:11]):
+            # An empty hex adds a of distance of 1. A hex of own color add distance 0. Opposite color adds infinite distance. 
+            Distance[start] = 1 if (board[v[0]][v[1]] == 0) else 0 if (board[v[0]][v[1]] == player) else math.inf
+        visited = set() # Also called sptSet, short for "shortest path tree Set"
+        while len(ALL_SET.difference(visited)): # While there are any un-visited hexes
+            # Find the next un-visited hex, that has the lowest distance
+            remainingHexes = ALL_SET.difference(visited)
+            A = [Distance[k] for k in remainingHexes] # Find the distance to each un-visited hex
+            u = list(remainingHexes)[A.index(min(A))] # Chooses the one with the lowest distance
+            
+            # Find neighbors of the hex u
+            for di in HEX_DIRECTIONS:
+                v = (u[0] + di[0] , u[1] + di[1]) # v is a neighbor of u
+                if v[0] in range(11) and v[1] in range(11) and v not in visited:
+                    new_dist = Distance[u] + (1 if (board[v[0]][v[1]] == 0) else 0 if (board[v[0]][v[1]] == player) else math.inf)
+                    Distance[v] = min(Distance[v], new_dist)
+
+                    # If at the goal and the distance is still 0, we've won!
+                    if new_dist == 0 and v[player-1] == 10: # if the right coordinate of v is 10, it means we're at the goal
+                        isWon = True
+                        break
+            if isWon:
+                score[player] = math.inf # Winner!
+                score[player%2 +1] = -math.inf # loser!
+                break
+            # After a hex has been visited, this is noted
+            visited.add(u)
+            logThis("Distance from player {}'s start to {} is {}".format(player,u,Distance[u]))
+        # When all hexes on the board have been checked:
+        score = # the minimum distance of the row of the goal
+
+    return score, isWon
 
-    return won, winningPieces
 
 # Plays as the AI
 def hexAI(channel):
@@ -257,33 +297,6 @@ def hexAI(channel):
     placement = "abcdefghijk"[chosenMove[1]]+str(chosenMove[0]+1)
     return placeHex(channel,placement, "Gwendolyn")
 
-# Calculates points for a board
-def AICalcHexPoints(board,player):
-    score = 0
-    #otherPlayer = player%2+1
-
-    
-    ## Checks if anyone has won
-    #won = isHexWon(board)[0]
-
-    ## Add points if AI wins
-    #if won == player:
-    #    score += AIScoresHex["win"]
-
-    return score
-
-
-#def evaluateWindow(window,player,otherPlayer):
-#    if window.count(player) == 4:
-#        return AIScoresHex["win"]
-#    elif window.count(player) == 3 and window.count(0) == 1:
-#        return AIScoresHex["three in a row"]
-#    elif window.count(player) == 2 and window.count(0) == 2:
-#        return AIScoresHex["two in a row"]
-#    elif window.count(otherPlayer) == 4:
-#        return AIScoresHex["enemy win"]
-#    else:
-#        return 0
 
 def minimaxHex(board, depth, player , originalPlayer, alpha, beta, maximizingPlayer):
     terminal = ((isHexWon(board)[0] != 0) or (0 not in board[0]))