Data update

Task/Entropy/Rust/entropy.rs

@@ -0,0 +1,20 @@
+fn entropy(s: &[u8]) -> f32 {
+    let mut histogram = [0u64; 256];
+
+    for &b in s {
+        histogram[b as usize] += 1;
+    }
+
+    histogram
+        .iter()
+        .cloned()
+        .filter(|&h| h != 0)
+        .map(|h| h as f32 / s.len() as f32)
+        .map(|ratio| -ratio * ratio.log2())
+        .sum()
+}
+
+fn main() {
+    let arg = std::env::args().nth(1).expect("Need a string.");
+    println!("Entropy of {} is {}.", arg, entropy(arg.as_bytes()));
+}