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ROSECODE 414

Convex numbers

sinan · Programming ·

Take the number 134431001 as an example. We can make pairs using the 2 digits following one another: [(1, 3), (3, 4), (4, 4), (4, 3), (3, 1), (1, 0), (0, 0), (0, 1)] If we assume that these are the lattice points, we can draw line segments in the same order and we can have a polygon. In general for a k-digit number like d1d2...dk we can have a (k-1)-gon: [(d1,d2), (d2,d3), ..., (dk-1,dk)] If the drawn polygon is a convex one then we will call this kind of number as convex number. How many positive convex numbers are there? Answer format: count,sum [My timing: < 1m] Notes: - Any two neighbouring line segments cannot be collinear. - All the generated pairs must be distinct. - Some polygons can be generated by more than one number. For example: 112321, 123211, 232112, 321123, 211232 Since the numbers are different, they are all counted.