Question

First off, this is part of an extra credit homework, so please do not give me the answer. Please just help me understand where I might have a problem with what is going on. It is a Tic-Tac-Toe generator where the game goes through recursively to determine the best move based on the player. (Professor uses white ‘W’ and black ‘B’ instead of X and O)

My main recursive method returns the state score based on an input position on the TTT board; 1 if white will force a win from that position, 0 if it is a draw, and -1 if black will force a win from that position:

public int stateScore(boolean whiteMove, int[] BestMove) {
    return stateScore(whiteMove,BestMove,TTTBoard);
}

which calls my underlying private recursion method:

private int stateScore(boolean whiteMove, int[] BestMove,char[][] TestBoard) {
    char [][] newTestBoard = new char [3][3];
    for(int rowVal = 0; rowVal < 3; rowVal++){
        for(int colVal = 0; colVal < 3; colVal++){
            newTestBoard[rowVal][colVal] = TestBoard[rowVal][colVal];
        }
    }

    int [] bestMove = new int [2];

    for(int rowVal = 0; rowVal < 3; rowVal++){
        for(int colVal = 0; colVal < 3; colVal++){
            if(isFull(newTestBoard) == true){
                return 0;
            }
            else if(newTestBoard[rowVal][colVal] == '-'){
                bestMove[0] = rowVal;
                bestMove[1] = colVal;

                //if boolean is white
                 if(whiteMove == true){
                    newTestBoard = testEntry(rowVal,colVal,'W',newTestBoard);
                    if(threeInRow(newTestBoard) == 1){
                        return 1;
                    }
                    else if(threeInRow(newTestBoard) == 0 && isFull(newTestBoard) == true){
                        return 0;
                    }
                    else if(threeInRow(newTestBoard) == -1 && isFull(newTestBoard) == true){
                        return -1;
                    }
                    else{
                        return stateScore(!whiteMove,bestMove,newTestBoard);
                    }
                }
                //if boolean is black
                else{
                    newTestBoard = testEntry(rowVal,colVal,'B',newTestBoard);
                    if(threeInRow(newTestBoard) == -1){
                        return -1;
                    }
                    else if(threeInRow(newTestBoard) == 0 && isFull(newTestBoard) == true){
                        return 0;
                    }
                    else if(threeInRow(newTestBoard) == 1 && isFull(newTestBoard) == true){
                        return 1;
                    }
                    else{
                        return stateScore(!whiteMove,bestMove);
                    }
                }
            }
        }
    }
    return 0;
}

The boolean value for whiteMove is true if it is white’s move, and false if it is black’s. Secondary methods within the function include threeInRow:

public int threeInRow(char[][] TTTBoard){
    boolean whiteIs = false;
    boolean blackIs = false;
        //Horizontal?
        char [] colChar = new char [3];
        for(int rowVal = 0; rowVal < 3; rowVal ++){
            for(int colVal = 0; colVal < 3; colVal++){
                colChar[colVal] = TTTBoard[rowVal][colVal];
            }
            if(colChar[0] == colChar[1] && colChar[1] == colChar[2]){
                if(colChar[0] == 'W'){
                    whiteIs = true;
                }
                if(colChar[0] == 'B'){
                    blackIs = true;
                }
            }
        }

        //Vertical?
        char [] rowChar = new char [3];
        for(int colVal = 0; colVal < 3; colVal ++){
            for(int rowVal = 0; rowVal < 3; rowVal++){
                rowChar[colVal] = TTTBoard[rowVal][colVal];
            }
            if(rowChar[0] == rowChar[1] && rowChar[1] == rowChar[2]){
                if(rowChar[0] == 'W'){
                    whiteIs = true;
                }
                else if(rowChar[0] == 'B'){
                    blackIs = true;
                }
            }
        }

        //Diagonal
            //topLeft to bottomRight
            if(TTTBoard[0][0] == TTTBoard[1][1] && TTTBoard[1][1] == TTTBoard[2][2]){
                if(TTTBoard[0][0] == 'W'){
                    whiteIs = true; 
                }
                else if(TTTBoard[0][0] == 'B'){
                    blackIs = true;
                }
            }

            //topRight to bottomLeft
            if(TTTBoard[0][2] == TTTBoard[1][1] && TTTBoard[1][1] == TTTBoard [2][0]){
                if(TTTBoard[1][1] == 'W'){
                    whiteIs = true;
                }
                else if(TTTBoard[1][1] == 'B'){
                    blackIs = true;
                }
            }


    //Return Vals
    if(whiteIs == true && blackIs == true){
        return 0;
    }
    else if(blackIs == true && whiteIs == false){
        return -1;
    }
    else if(blackIs == false && whiteIs == true){
        return 1;
    }
    else if(blackIs == false && whiteIs == false){
        return 0;
    }
    else{
        return 0;
    }

}

and testEntry:

public char[][] testEntry(int row,int col,char newChar, char[][] TestBoard){

    char [][] returnBoard = new char[3][3];
    for(int rowVal = 0; rowVal < 3; rowVal++){
        for(int colVal = 0; colVal < 3; colVal++){
            returnBoard[rowVal][colVal] = TestBoard[rowVal][colVal];
        }
    }
    returnBoard[row][col] = newChar;
    return returnBoard;

}

I don’t understand where the stack overflow is coming from. It seems as though my returns cover all cases, and that my methods have appropriate returns. I haven’t ever used a for loop with recursion, am I messing something up with that. Also, I am correct in saying that type [] name = name (same type) does NOT work, right? That is why I did the for loops in that case.

Answer 1

In your black branch your return is wrong.

You return

return stateScore(!whiteMove,bestMove);

which restarts the recursion. You want to return

return stateScore(!whiteMove,bestMove,newTestBoard);

Hints:

• Fix your booleans:

  if(whiteMove == true) -> if (whiteMove)
  

• Use UpperCase for Classes, lowerCamelCase for variables.

• If you return in an if branch, then you don’t need an else.

  Instead of:

  if (condition) {
    ...
    return ...;
  }
  else
  {
    ...
  }
  

  It is better to write:

  if (condition) {
    ...
    return ...;
  }
  ...
  

  Keeps the nesting lower and makes the code easier to follow.

• Refactor common code: Both branches return the same result:

  return stateScore(!whiteMove,bestMove,newTestBoard);
  

  Why not move this outside the if (whiteMove)