This is somewhat OT but I think it's an interesting problem. Consider
the following data:
double[][] a =
[
[ 1, 4, 7, 8 ],
[ 1, 7 ],
[ 1, 7, 8],
[ 4 ],
[ 7 ],
];
We want to compute an n-way union, i.e., efficiently span all elements
in all arrays in a, in sorted order. You can assume that each individual
array in a is sorted. The output of n-way union should be:
auto witness = [
1, 1, 1, 4, 4, 7, 7, 7, 7, 8, 8
];
assert(equal(nWayUnion(a), witness[]));
The STL and std.algorithm have set_union that does that for two sets:
for example, set_union(a[0], a[1]) outputs [ 1, 1, 4, 7, 7, 8 ]. But
n-way unions poses additional challenges. What would be a fast
algorithm? (Imagine a could be a very large range of ranges).
Needless to say, nWayUnion is a range :o).
Finally, why would anyone care for something like this?
Andrei
