Add an example for ABC145-C

qryxip · qryxip · commit b393f3b5be5f · 2020-05-19T00:20:08.000+09:00
diff --git a/examples/abc145-c.rs b/examples/abc145-c.rs
@@ -0,0 +1,53 @@
+// https://atcoder.jp/contests/abc145/tasks/abc145_c
+//
+// 以下のクレートを使用。
+//
+// - `itertools`
+// - `nalgebra`
+// - `proconio`
+
+use itertools::Itertools as _;
+use nalgebra::{Point2, Scalar};
+use proconio::input;
+use proconio::source::{Readable, Source};
+
+use std::convert::Infallible;
+use std::io::BufRead;
+use std::marker::PhantomData;
+
+fn main() {
+    // `proconio::input!`。
+    //
+    // https://docs.rs/proconio/0.3.6/proconio/macro.input.html
+    input! {
+        n: usize,
+        points: [ReadPoint2<f64>; n],
+    }
+
+    // nC2通りの組み合わせを列挙するのに`<_ as itertools::Itertools>::tuple_combinations`を用いる。
+    // また各点同士の距離√((x_i - x_j)^2 + (y_i - y_j)^2)を求めるのに`nalgebra::distance`を使う。
+    //
+    // https://docs.rs/itertools/0.8/itertools/trait.Itertools.html#method.tuple_combinations
+    // https://docs.rs/nalgebra/0.19/nalgebra/fn.distance.html
+    let ans = 2.0 / (n as f64)
+        * points
+            .into_iter()
+            .tuple_combinations()
+            .map(|(p1, p2)| nalgebra::distance(&p1, &p2))
+            .sum::<f64>();
+    println!("{}", ans);
+}
+
+// `proconio::source::Readable`を実装することで`Usize1`のようなマーカー型を作ることができる。
+//
+// https://docs.rs/proconio/0.3.6/proconio/source/trait.Readable.html
+
+struct ReadPoint2<T>(Infallible, PhantomData<fn() -> T>);
+
+impl<N: Readable<Output = N> + Scalar> Readable for ReadPoint2<N> {
+    type Output = Point2<N>;
+
+    fn read<R: BufRead, S: Source<R>>(source: &mut S) -> Point2<N> {
+        Point2::new(N::read(source), N::read(source))
+    }
+}
diff --git a/test-examples.toml b/test-examples.toml
@@ -142,6 +142,13 @@ url = "https://atcoder.jp/contests/abc144/tasks/abc144_d"
 matching = { FloatOr = { abs = 1e-6, rel = 1e-6 } }
 meta = { using = ["libm", "proconio"] }
 
+[examples.abc145-c]
+type = "Normal"
+name = "ABC145: C - Average Length"
+url = "https://atcoder.jp/contests/abc145/tasks/abc145_c"
+matching = { FloatOr = { abs = 1e-6, rel = 1e-6 } }
+meta = { using = ["itertools", "nalgebra", "proconio"] }
+
 [examples.abc150-d]
 type = "Normal"
 name = "ABC150: D - Semi Common Multiple"
