Given,
f(x)=minx−[x],1+[x]−x
So, the graph of the function is

1−x=1−x;0≤x<1

From the graph we can say that the function is continuous at all points in the interval [0,3].
So, P=0
Again, from the diagram, we can say that at x=21,1,23,2,25, there are sharp edges.
So, the function is non differentiable at x=21,1,23,2,25
Hence, Q=5
So, P+Q=5