CTCI 17.2

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

CTCI 17.2.java

public static Piece hasWon(Piece[][] board){
    //test row
    for(int i = 0; i < board.length; i++){
        if(board[i][0] == Piece.EMPTY) continue;
        for(int j = 1; j < board[0].length; j++){
            if(board[i][j] != board[i][j - 1]) break;
            if(j == board[0].length - 1) return board[i][0];
        }
    }
    
    //test column
    for(int i = 0; i < board[0].length; i++){
        if(board[0][i] == Piece.EMPTY) continue;
        for(int j = 1; j < board.length; j++){
            if(board[j][i] != board[j - 1][i]) break;
            if(j == board.length - 1) return board[0][i];
        }
    }
    
    //test diagonal (top left -> bottom right)
    if(board[0][0] != Piece.Empty){
        for(int diagonal = 1; diagonal < board.length; diagonal++){
            if(board[diagonal][diagonal] != board[diagonal - 1][diagonal - 1]) break;
            if(diagonal == board.length - 1) return board[0][0];
        }
    }
    
    //test diagonal (top right -> bottom left)
    if(board[0][board[0].length - 1] != Piece.Empty){
        for(int diagonal = 1; diagonal < board.length; diagonal++){
            if(board[diagonal][board[0].length - 1 - diagonal] != board[diagonal - 1][board[0].length - 1 - diagonal - 1]) break;
            if(diagonal == board.length - 1) return board[0][0];
        }
    }
    
    return Piece.EMPTY;
}

public enum Piece{
    EMPTY, BLACK, WHITE
}