function w = solver(b)

% connect immediate neighbors vertically
[r, c] = find(b(1:end-1,:) == b(2:end,:) & b(1:end-1,:));
w = [r, c, r+1, c];

% connect immediate neighbors horizontally
[r, c] = find(b(:,1:end-1) == b(:,2:end) & b(:,1:end-1));
w = [w; r, c, r, c+1];