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Find Winner on a Tic Tac Toe Game

Tic-tac-toe is played by two players A and B on a 3 x 3 grid.

Here are the rules of Tic-Tac-Toe:

Players take turns placing characters into empty squares (" "). The first player A always places "X" characters, while the second player B always places "O" characters. "X" and "O" characters are always placed into empty squares, never on filled ones. The game ends when there are 3 of the same (non-empty) character filling any row, column, or diagonal. The game also ends if all squares are non-empty. No more moves can be played if the game is over. Given an array moves where each element is another array of size 2 corresponding to the row and column of the grid where they mark their respective character in the order in which A and B play.

Return the winner of the game if it exists (A or B), in case the game ends in a draw return "Draw", if there are still movements to play return "Pending".

You can assume that moves is valid (It follows the rules of Tic-Tac-Toe), the grid is initially empty and A will play first.

Example 1:

Input: moves = [[0,0],[2,0],[1,1],[2,1],[2,2]]
Output: "A"
Explanation: "A" wins, he always plays first.

[X][ ][ ]
[ ][ ][ ]
[ ][ ][ ]

[X][ ][ ]
[ ][ ][ ]
[O][ ][ ]

[X][ ][ ]
[ ][X][ ]
[O][ ][ ]

[X][ ][ ]
[ ][X][ ]
[O][O][ ]

[X][ ][ ]
[ ][X][ ]
[O][O][X]

Example 2:

Input: moves = [[0,0],[1,1],[0,1],[0,2],[1,0],[2,0]]
Output: "B"
Explanation: "B" wins.

[X][X][O]
[X][O][ ]
[O][ ][ ]

Example 3:

Input: moves = [[0,0],[1,1],[2,0],[1,0],[1,2],[2,1],[0,1],[0,2],[2,2]]
Output: "Draw"
Explanation: The game ends in a draw since there are no moves to make.

[X][X][O]
[O][O][X]
[X][O][X]

Example 4:

Input: moves = [[0,0],[1,1]]
Output: "Pending"
Explanation: The game has not finished yet.
[X][ ][ ]
[ ][O][ ]
[ ][ ][ ]

Constraints:

1 <= moves.length <= 9
moves[i].length == 2
0 <= moves[i][j] <= 2
There are no repeated elements on moves.
moves follow the rules of tic tac toe.

Prerequisites

Ruby > 2.0

bundler

From the solutions/ruby folder with

bundle install

# run the tests with
ruby -I lib:test tic_tac_test.rb --verbose