added win conditions to check_winner in game.py

What I changed
I added the 8 possible tic-tac-toe win conditions to check_winner and
compare the values in the state with the symbol passed to the method

Why I changed it
It took a WHILE to figure out how to actually read the current state of
the game, but once I had that, I was able to figure out how to check
it for the symbol being sought.

Estimate for remaining time to finish assignment: [1 hour?]
I thought it was "how long did it take" now "how long remaining" originally.

ttt/game.py

@@ -26,6 +26,7 @@ class TTTGame:
 
     def is_over(self, state):
         "Checks whether the game is over."
+                # FALSE because blank           FALSE because no markers        FALSE because no markers
         return self.board_is_full(state) or self.check_winner(state, 'X') or self.check_winner(state, 'O')
 
     def get_reward(self, state):
@@ -58,4 +59,17 @@ class TTTGame:
 
     def check_winner(self, state, symbol):
         "Checks whether the player with `symbol` has won the game."
+        currentState = state["board"]
+        # possible tic tac toes: 012 345 678 036 147 258 048 246
+        for i in range(0,7,3):
+            if currentState[i] == symbol and currentState[i+1] == symbol and currentState[i+2] == symbol:
+                return True
+        for i in range(3):
+            if currentState[i] == symbol and currentState[i+3] == symbol and currentState[i+6] == symbol:
+                return True
+        if currentState[0] == symbol and currentState[4] == symbol and currentState[8] == symbol:
+            return True
+        if currentState[2] == symbol and currentState[4] == symbol and currentState[6] == symbol:
+            return True
+        
         return False