int r = rand();
     int n = r % p;
     while ( a[n] != 0 ) {
         n = (n + n) % p;
     }
     a[n] = r;

##</code><code>##

say (($_ + 5) % 11 ) for (0..10);

5
6
7
8
9
10
0
1
2
3
4