Reversi move simulation with captures in 8 directions

Implement one move of the board game Reversi (also sold as Othello).

You get an n x n board as a list of lists of characters. Each cell is 'B' (black), 'W' (white) or '.' (empty). You also get row, col and player ('B' or 'W').

Write make_move(board, row, col, player) that returns the board after player tries to place a piece at (row, col).

Rules

• Look from (row, col) in each of the 8 directions (horizontal, vertical, diagonal).
• A direction captures when it holds one or more consecutive opponent pieces followed directly by a player piece. An empty cell or the board edge before the closing piece means no capture in that direction.
• If at least one direction captures, place the piece and flip every captured opponent piece in every capturing direction to player.
• If the cell is occupied, off the board, or no direction captures, the move is illegal: return the board unchanged.
• Do not modify the input board; return a new one.

Constraints

• 1 <= n <= 100
• player is 'B' or 'W'.

Example 1

board  = [".WWB",
          "WW..",
          "B.B.",
          "...."]
row = 0, col = 0, player = 'B'

Output:

["BBBB",
 "BB..",
 "B.B.",
 "...."]

The run to the right closes on (0, 3), the run down closes on (2, 0), and the diagonal closes on (2, 2), so all four white pieces flip.

Example 2

board  = [".WW",
          "...",
          "..."]
row = 0, col = 0, player = 'B'

Output: the same board. The white run reaches the edge without a black piece to close it, so the move is illegal.

Reconstructed from the reported question; details may differ from what interviewers ask.