text: traverses column wise
code: for i in range ( m ) : NEW_LINE INDENT u = 0 NEW_LINE v = 0 NEW_LINE for j in range ( n ) : NEW_LINE INDENT if a [ j ] [ i ] : NEW_LINE INDENT u += 1 NEW_LINE DEDENT else : NEW_LINE INDENT v += 1 NEW_LINE DEDENT DEDENT res += pow ( 2 , u ) - 1 + pow ( 2 , v ) - 1 NEW_LINE DEDENT