31 lines
719 B
D
31 lines
719 B
D
import std.stdio, std.random, std.algorithm;
|
|
|
|
struct SOfN(int n) {
|
|
size_t i;
|
|
int[n] sample = void;
|
|
static rng = Xorshift(0);
|
|
|
|
int[] next(in int item) {
|
|
i++;
|
|
if (i <= n)
|
|
sample[i - 1] = item;
|
|
else if (uniform(0.0, 1.0, rng) < (cast(double)n / i))
|
|
sample[uniform(0, n, rng)] = item;
|
|
return sample[0 .. min(i, $)];
|
|
}
|
|
}
|
|
|
|
void main() {
|
|
enum nRuns = 100_000;
|
|
size_t[10] bin;
|
|
|
|
foreach (trial; 0 .. nRuns) {
|
|
SOfN!(3) sofn;
|
|
foreach (item; 0 .. bin.length - 1)
|
|
sofn.next(item);
|
|
foreach (s; sofn.next(bin.length - 1))
|
|
bin[s]++;
|
|
}
|
|
writefln("Item counts for %d runs:\n%s", nRuns, bin);
|
|
}
|