The initial problem: for a given 3x3 tic tac toe board check if one of the players has won.
The simplest solution I have come up so far is rotating the matrix and summing up each row:
board
[[0, 1, 2], [3, 4, 5], [6, 7, 8]]
pr(board)
0 1 2
3 4 5
6 7 8
pr(zip(*board))
0 3 6
1 4 7
2 5 8
0..9 numbers above are just for showing positions on the board, normally they would be filled with 1 for player 1 and -1 for player 2 and 0 for unfilled position. Go row by row and if it sums up to 3 or -3 this is the winning block.
However, diagonals are not checked. Is there some way to extract diagonals from such matrix in elegant + highly performant way? I don't mean using trivial indexes "manually" (0, 1, 2), but rather get diagonal of n x n matrix.
P.S. pr is just a helper function for printing 2d list:
def pr(x):
for row in x:
print ' '.join(map(str, row))
Number your game field with a magic square
2|9|4
7|5|3
6|1|8
Now sum up after three moves and check if the sum is 15 --> Winner. You have to check this for every player. Surely you have to recheck after 4th move and 5th move (only the player that started the game)
This is how I solved this problem in my first Java class.