June 2018 Update

Task/Unbias-a-random-generator/Rust/unbias-a-random-generator.rust

@@ -0,0 +1,39 @@
+#![feature(inclusive_range_syntax)]
+
+extern crate rand;
+
+use rand::Rng;
+
+fn rand_n<R: Rng>(rng: &mut R, n: u32) -> usize {
+    rng.gen_weighted_bool(n) as usize // maps `false` to 0 and `true` to 1
+}
+
+fn unbiased<R: Rng>(rng: &mut R, n: u32) -> usize {
+    let mut bit = rand_n(rng, n);
+    while bit == rand_n(rng, n) {
+        bit = rand_n(rng, n);
+    }
+    bit
+}
+
+fn main() {
+    const SAMPLES: usize = 100_000;
+    let mut rng = rand::weak_rng();
+
+    println!(" Bias    rand_n  unbiased");
+    for n in 3..=6 {
+        let mut count_biased = 0;
+        let mut count_unbiased = 0;
+        for _ in 0..SAMPLES {
+            count_biased += rand_n(&mut rng, n);
+            count_unbiased += unbiased(&mut rng, n);
+        }
+
+        let b_percentage = 100.0 * count_biased as f64 / SAMPLES as f64;
+        let ub_percentage = 100.0 * count_unbiased as f64 / SAMPLES as f64;
+        println!(
+            "bias {}:  {:0.2}%   {:0.2}%",
+            n, b_percentage, ub_percentage
+        );
+    }
+}