# Boolean expressions from Bubble Diagram for D-flip flop entries

I am supposed to get boolean expressions for the two D-flip flops involved in this state diagram but I am stuck.

I have come up with a truth table (except for output y which I don't understand) for the state diagram but I don't understand how to get the actual expressions of D0 and D1. The hindsight says: D1 = 0, D0 = Q1'Q0'+xQ1Q0+x'Q'0 but I don't know how to get there, I'm struggling with the truth table

How do I do it? This is my truth table based on S0, S1, S2 and S3:

$$\begin{array}{ccc|ccc} & PS & & & NS \\ D0 & D1 & x & D0 & D1 & y \\ \hline 0 & 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 & 1 \\ 0 & 1 & 0 & 0 & 0 \\ 0 & 1 & 1 & 0 & 0 \\ 1 & 0 & 0 & 0 & 1 \\ 1 & 0 & 1 & 0 & 0 \\ 1 & 1 & 0 & 0 & 0 \\ 1 & 1 & 1 & 0 & 1 \\ \end{array}$$