How to draw quark flow diagram when no flavour change occurs? I've been asked to draw the quark flow diagram for $K^-p\rightarrow \pi^-\Sigma^+$, I did it like this:

(Apologies for the handwriting)
As you can see, I basically assumed that since the initial and final state actually contain all of the same flavours of quarks, the diagram would simply consist of lines connecting them.
My lecturer however, drew this version:

Is there some rule about how to handle this situation? What makes my attempt wrong? I have tried to read a bit about quark flow diagrams but have not found much information. Any advice is much appreciated!
 A: You missed one important point of quark flow diagrams (see also Feynman diagram):
Normal particles ($u$, $d$, $s$) have their arrows pointing from past to future.
But anti-particles ($\bar u$, $\bar d$, $\bar s$) have their arrows pointing from future to past.
Hence you would begin to draw the diagram like this:

Then you look how you can connect the lines
while taking care of the arrow directions.
There are actually severeral possible ways.
One way is how your lecturer did (diagram 1).  

But another way is also possible (diagram 2):


To find out which of the processes shown above is
more likely to happen, we can use this rule of thumb
as given by CERN Indico - Drawing Feynman Diagrams
(paragraph 13):

To get an idea of the probability of a Feynman diagram,
    we count the number of vertices (another word for
    interaction points). The more, the less probable. 

According to the Feynman rules of QCD
we need to add gluons (the curly green lines)
for mediating the interaction between quarks.
The interaction points are marked as $\color{green}{\bullet}$.
(I'm not completely sure about where to place the gluons
in the following Feynman diagrams. So other people with
more knowledge in QCD may point out my mistakes.)
In diagram (1) we need 4 gluons with 8 interaction points.

In diagram (2) we also need 4 gluons with 8 interaction points.

Therefore we conclude that the processes from diagram (1)
and diagram (2) occur with similar probabilities.
