The sequence is generated by following this pseudo-code:

A:  The first term is zero.
    Repeatedly apply:
        If the last term is *new* to the sequence so far then:
B:          The next term is zero.
        Otherwise:
C:          The next term is how far back this last term occured previously.



Example

Using A:

0
Using B:

0 0
Using C:

0 0 1
Using B:

0 0 1 0
Using C: (zero last occurred two steps back - before the one)

0 0 1 0 2
Using B:

0 0 1 0 2 0
Using C: (two last occurred two steps back - before the zero)

0 0 1 0 2 0 2 2
Using C: (two last occurred one step back)

0 0 1 0 2 0 2 2 1
Using C: (one last appeared six steps back)

0 0 1 0 2 0 2 2 1 6
...



Task

 Create a function/procedure/method/subroutine/... to generate the Van Eck sequence of numbers.
 Use it to display here, on this page:
 The first ten terms of the sequence.
 Terms 991 - to - 1000 of the sequence.


References

 Don't Know (the Van Eck Sequence) - Numberphile video.
 Wikipedia Article: Van Eck's Sequence.
  OEIS sequence: A181391.


fn main() {
    max := 1000
    mut a := []int{len: max} // all zero by default
    for n in 0..max-1 {
        for m := n - 1;  m >= 0; m-- {
            if a[m] == a[n] {
                a[n+1] = n - m
                break
            }    
        }
    }
    println("The first ten terms of the Van Eck sequence are:")
    println(a[..10])
    println("\nTerms 991 to 1000 of the sequence are:")
    println(a[990..])
}