Check if someone has won tic-tac-toe

Problem

Design an algorithm to figure out if someone has won in a game of tic-tac-toe.

Solution

I’ve written a game of tic-tac-toe in Java, and my current method of determining the end of the game accounts for the following possible scenarios for the game being over:

The board is full, and no winner has yet been declared: Game is a draw.
Cross has won.
Circle has won.

Suppose instead of 9 space, 2D matrix we have nXn matrix.
We know a winning move can only happen after X or O has made their most recent move, so you can only search row/column with optional diag that are contained in that move to limit your search space when trying to determine a winning board. Also since there are a fixed number of moves in a draw tic-tac-toe game once the last move is made if it wasn’t a winning move it’s by default a draw game.

public class TicTacToe {  
  
    enum State{Blank, X, O};  
  
    int n = 3;  
    State\[\]\[\] board = new State\[n\]\[n\];  
    int moveCount;  
  
    void Move(int x, int y, State s){  
     if(board\[x\]\[y\] == State.Blank){  
      board\[x\]\[y\] = s;  
     }  
     moveCount++;  
  
     //check end conditions  
  
     //check col  
     for(int i = 0; i < n; i++){  
      if(board\[x\]\[i\] != s)  
       break;  
      if(i == n-1){  
       //report win for s  
      }  
     }  
  
     //check row  
     for(int i = 0; i < n; i++){  
      if(board\[i\]\[y\] != s)  
       break;  
      if(i == n-1){  
       //report win for s  
      }  
     }  
  
     //check diag  
     if(x == y){  
      //we're on a diagonal  
      for(int i = 0; i < n; i++){  
       if(board\[i\]\[i\] != s)  
        break;  
       if(i == n-1){  
        //report win for s  
       }  
      }  
     }  
  
            //check anti diag (thanks rampion)  
     for(int i = 0;i<n;i++){  
      if(board\[i\]\[(n-1)-i\] != s)  
       break;  
      if(i == n-1){  
       //report win for s  
      }  
     }  
  
     //check draw  
     if(moveCount == (n^2 - 1)){  
      //report draw  
     }  
    }  
}

References

Problem

Solution

See also