015 ok

015/main.rs

@@ -0,0 +1,29 @@
+type LS = Vec<Vec<Option<u64>>>;
+
+struct Lattice { ls: LS }
+
+impl Lattice {
+    pub fn new() -> Lattice {
+        let mut ls = LS::new();
+        for _i in 0..21 {
+            let lr = vec![None; 21];
+            ls.push(lr);
+        }
+        ls[0][0] = Some(1);
+        Lattice { ls: ls }
+    }
+    pub fn compute(&mut self, i: usize, j: usize) -> u64 {
+        if self.ls[i][j].is_some() { return self.ls[i][j].unwrap(); }
+        let mut res = 0u64;
+        if i > 0 { res += self.compute(i - 1, j); }
+        if j > 0 { res += self.compute(i, j - 1); }
+        self.ls[i][j] = Some(res);
+        res
+    }
+}
+
+fn main() {
+    let mut lt = Lattice::new();
+    let res = lt.compute(20, 20);
+    println!("{}", res);
+}