Calculate good and bad shifts
for i in range ( 1 , k + 1 ) : NEW_LINE INDENT dp1 [ i ] = ( ( dp1 [ i - 1 ] * ( a - 1 ) ) % mod + ( dp2 [ i - 1 ] * a ) % mod ) % mod NEW_LINE dp2 [ i ] = ( ( dp1 [ i - 1 ] * ( b ) ) % mod + ( dp2 [ i - 1 ] * ( b - 1 ) ) % mod ) % mod NEW_LINE DEDENT