Add an example for ABC154-E

qryxip · qryxip · commit 844328346c81 · 2020-05-19T00:20:08.000+09:00
diff --git a/examples/abc154-e.rs b/examples/abc154-e.rs
@@ -0,0 +1,52 @@
+// https://atcoder.jp/contests/abc154/tasks/abc154_e
+//
+// 以下のクレートを使用。
+//
+// - `num`
+// - `proconio`
+
+use proconio::input;
+use proconio::marker::Bytes;
+
+fn main() {
+    // http://drken1215.hatenablog.com/entry/2020/02/09/225300
+
+    // `proconio::input!`。
+    //
+    // https://docs.rs/proconio/0.3.6/proconio/macro.input.html
+    input! {
+        n: Bytes,
+        k: usize,
+    }
+
+    let n = n.into_iter().map(|d| (d - b'0').into()).collect();
+
+    println!("{}", St { n }.solve(0, k, false));
+
+    struct St {
+        n: Vec<usize>,
+    }
+
+    impl St {
+        fn solve(&self, i: usize, j: usize, p: bool) -> usize {
+            let Self { n } = self;
+
+            if j == 0 {
+                1
+            } else if i == n.len() {
+                0
+            } else if p {
+                // 配列でのDPと違い、ここで打ち切れる。 ここで`num_integer::binomial`が使える。
+                //
+                // https://docs.rs/num-integer/0.1/num_integer/fn.binomial.html
+                num::integer::binomial(n.len() - i, j) * 9usize.pow(j as u32)
+            } else if n[i] == 0 {
+                self.solve(i + 1, j, false)
+            } else {
+                self.solve(i + 1, j, true)
+                    + self.solve(i + 1, j - 1, true) * (n[i] - 1)
+                    + self.solve(i + 1, j - 1, false)
+            }
+        }
+    }
+}
diff --git a/test-examples.toml b/test-examples.toml
@@ -163,6 +163,13 @@ url = "https://atcoder.jp/contests/abc154/tasks/abc154_d"
 matching = { FloatOr = { abs = 1e-6, rel = 1e-6 } }
 meta = { using = ["itertools-num", "ordered-float", "proconio"] }
 
+[examples.abc154-e]
+type = "Normal"
+name = "ABC154: E - Almost Everywhere Zero"
+url = "https://atcoder.jp/contests/abc154/tasks/abc154_e"
+matching = "Words"
+meta = { using = ["num", "proconio"] }
+
 [examples.agc023-a]
 type = "Normal"
 name = "AGC023: A - Zero-Sum Ranges"
