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Find the in-between point
Description
For this kata, you are given three points (x1,y1,z1), (x2,y2,z2), and (x3,y3,z3) that lie on a straight line in 3-dimensional space.
You have to figure out which point lies in between the other two.
Your function should return 1, 2, or 3 to indicate which point is
the in-between one.