Efficient way of finding distance between two 3D points

Question

I am writing a code in C++ and want to compute distance between two points. Question 1:

I have two points P(x1, y1, z1) and Q(x2, y2, z2) , where x,

Answer 1

No, there is no more efficient way to calc the dist. Any treatment with special cases p.x==q.x etc. will be slower on average.

Yes, the fastest way to see if p and q are the same points is just comparing x, y, z. Since they are float, you should not check == but allow for some finite, small difference which you define.