014 basic

014/main.rs

@@ -0,0 +1,38 @@
+type CZS = Vec<Option<u32>>;
+struct Collatz { czs: CZS }
+
+impl Collatz {
+    pub fn new() -> Collatz {
+        let cl0 = Some(0); // for indexing
+        let cl1 = Some(1);
+        Collatz { czs: vec![cl0, cl1] }
+    }
+    pub fn compute(&mut self, n: usize) -> u32 {
+        match self.ensure_get(n) {
+            Some(cl) => cl,
+            None => {
+                //println!("compute {}", n);
+                let cl_prev = if n % 2 == 0 { 
+                    self.compute(n / 2)
+                } else {
+                    self.compute(3 * n + 1)
+                };
+                self.czs[n] = Some(cl_prev + 1);
+                cl_prev + 1
+            }
+        }
+    }
+    pub fn ensure_get(&mut self, i: usize) -> Option<u32> {
+        while self.czs.len() <= i { self.czs.push(None); }
+        self.czs[i]
+    }
+}
+
+fn main() {
+    let mut collatz = Collatz::new();
+
+    for k in 0..100000usize {
+        let clk = collatz.compute(k);
+        println!("{}: {}", k, clk);
+    }
+}