19. Symmetric about the $y$-axis, passing through the focus of the parabola $y^{2}=4 x$, and divided into two arcs with a length ratio of $1: 2$ by the line $y=x$, the equation of the circle is $\qquad$
$\begin{array}{l}\text { 19. } x^{2}+(y-1)^{2}=2 \text { or } x^{2} \\ +(y+1)^{2}=2\end{array}$