Problem 1698. Connect Four: find winning move

Inspired by this problem...

Connect Four is a fun two-player game in which the goal is to be the first player to connect four pieces in a row - horizontally, vertically, or diagonally. Players take turns dropping one of their pieces into any of the available columns.

Problem Statement

Given an array (size is arbitrary) in which

• 0 : space is empty
• 1 : player 1 piece
• 2 : player 2 piece

return the column that player 1 should play in to win the game. If there is more than one winning move, return a row vector of appropriate columns. If there are currently no winning moves, return [].

Assumptions

• Pieces fall to the bottommost available row in each column, as in the real game
• The input grid will always represent a valid game state

Example

If

b = [0 0 0 0 0 0 0;
     0 0 0 0 0 0 0;
     0 0 0 2 0 0 0;
     0 0 0 1 0 0 0;
     0 0 0 2 2 0 0;
     0 0 2 1 1 1 0];

then

y = 7