Checking Who Won Tic Tac Toe More Efficient C++

I'm writing a Tic Tac Toe Game and I would like to know how I can make an efficient function to check who won. A two dimensional array congaing X's, O's, or blank spaces represents the board.

  char CheckWin(const char board[][NUM_COLS], int& sum) // tic tac toe board - IN
{
    char tmp;
    int lcv;
    tmp = ' ';

    if (sum == 9)
    {
        return 'T';
    }
    else if (sum != 9)
    {
        if (((tmp = board[1][1]) != ' ' && board[0][0] == tmp && board[2][2] == tmp) || (board[2][0] == tmp &&开发者_Python百科amp; board[0][2] == tmp))
        {
            return tmp;
        }

        for (lcv = 0; lcv < 3; lcv++)
        {
            if ((tmp = board[lcv][0]) != ' ' && board[lcv][1] == tmp && board[lcv][2] == tmp)
            {
                return tmp;
            }
            else if ((tmp = board[lcv][0]) != ' ' && board[lcv][1] == tmp && board[lcv][2] == tmp)
            {
                return tmp;
            }
        }
    }

    return 'N';
}

Besides doing something similar to this over and over again, how could I check who won and return an X if X has won, an O if O has one, a T if it's a tie, and N if no one has one yet. Thanks in advance. I'm trying to get familiar with C++ and programming in general still.

EDIT: I just went with the simple method, but I somehow messed it up, anybody know how? It looks like it's not return anything because when I call it in the main after a player picks a row and column(that's working fine), it doesn't output anything

You could convert the array into two nine-bit values, one for the O positions and one for the X position, and a count of blank spaces:

x_mask = 0
y_mask = 0
empty_count = 0
mask = 1
for each square
  if x then x_mask |= mask
  if y then y_mask |= mask
  if empty then empty_count++
  mask <<= 1

Then compare the x_mask and y_mask against the eight possible winning combinations:

for each player
  for each winning combination
    if player_mask & winning_mask == winning_mask then player has won

and then handle the cases neither player has won:

if neither player won
  if empty_count == 0
    its a tie
  else
    moves still available

A simple "structured" approach

If you think of the board as:

A  B  C
D  E  F
G  H  I

Then one minimal selection of boxes that any winning layout must touch would be:

A B C
D
G

You can conceive the movement from any of these locations in a winning line in terms of a shift of 0, 1 or -1 positions in each of the X and Y directions. We can list the movements that you'd need to check:

A: (++x) (++x, ++y) (++y)
B: (++y)
C: (++y) (--x, ++y)
D: (++x)
E: (++x)

In C++, you can create a list/vector of the x/y coordinates of the starting points and the +/-/0 x/y movement deltas shown above, then use three nested loops to evaluate each line across the board.

This is considerably more work than just hardcoding the two loops over x and y coordinates and the two diagonals (below), but it's a more algorithmic approach that might appeal intellectually: more like what you might have to do if you were handling a much bigger board.

Obvious brute force approach

For the record, that simpler approach would look like this:

int x;
for (row = 0; row < 3; ++row)
    if ((x = board[row][0]) != Empty &&
        board[row][1] == x && board[row][2] == x)
        return x;
// similar loop for columns...
...
// hardcode diagonals...
if ((x = board[1][1]) != Empty &&
    (board[0][0] == x && board[2][2] == x ||
     board[2][0] == x && board[0][2] == x))
    return x

I suppose you could assign each winning board possibility a number (basically a hash value) and then check if the current board matches any of the values in the table by generating its hash value. On the other hand, I wouldn't suggest spending too much time trying to make the CheckWin function super-efficient. Unless it's being called millions of times or something and needs to be really fast, spend your time on something else--it probably won't be a bottleneck.