Data commit

Task/Knuths-algorithm-S/Rust/knuths-algorithm-s.rust

@@ -0,0 +1,46 @@
+use rand::{Rng,weak_rng};
+
+struct SofN<R: Rng+Sized, T> {
+    rng: R,
+    sample: Vec<T>,
+    i: usize,
+    n: usize,
+}
+
+impl<R: Rng, T> SofN<R, T> {
+    fn new(rng: R, n: usize) -> Self {
+        SofN{rng, sample: Vec::new(), i: 0, n}
+    }
+
+    fn add(&mut self, item: T) {
+        self.i += 1;
+        if self.i <= self.n {
+            self.sample.push(item);
+        } else if self.rng.gen_range(0, self.i) < self.n {
+            self.sample[self.rng.gen_range(0, self.n)] = item;
+        }
+    }
+
+    fn sample(&self) -> &Vec<T> {
+        &self.sample
+    }
+}
+
+
+pub fn main() {
+    const MAX: usize = 10;
+    let mut bin: [i32; MAX] = Default::default();
+    for _ in 0..100000 {
+        let mut s_of_n = SofN::new(weak_rng(), 3);
+
+        for i in 0..MAX { s_of_n.add(i); }
+
+        for s in s_of_n.sample() {
+            bin[*s] += 1;
+        }
+    }
+
+    for (i, x) in bin.iter().enumerate() {
+        println!("frequency of {}: {}", i, x);
+    }
+}