結果

問題 No.758 VVVVV
ユーザー tottoripaper
提出日時 2018-12-25 15:55:48
言語 OCaml
(5.2.1)
結果
AC  
実行時間 73 ms / 2,000 ms
コード長 2,040 bytes
コンパイル時間 217 ms
コンパイル使用メモリ 21,760 KB
実行使用メモリ 14,592 KB
最終ジャッジ日時 2024-10-09 00:32:41
合計ジャッジ時間 2,361 ms
ジャッジサーバーID
(参考情報)
judge4 / judge2
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ファイルパターン 結果
sample AC * 3
other AC * 23
権限があれば一括ダウンロードができます

ソースコード

diff #
プレゼンテーションモードにする

let rec expt ( * ) e a n =
if n = 0 then
e
else if n land 1 = 1 then
a * expt ( * ) e (a * a) (n / 2)
else
expt ( * ) e (a * a) (n / 2)
let mod_expt a n mo = expt (fun x y -> x * y mod mo) 1 a n
let mod_inv a p = mod_expt a (p - 2) p
module Combination : sig
type t
val init : n:int -> modulo:int -> t
val fact : int -> t -> int
val inv_fact : int -> t -> int
val nPk : int -> int -> t -> int
val nCk : int -> int -> t -> int
val nHk : int -> int -> t -> int
end = struct
type t = int * int array * int array
let init ~n ~modulo =
let f = Array.make (n + 1) 0 in
let () =
f.(0) <- 1;
for i = 1 to n do
f.(i) <- f.(i - 1) * i mod modulo
done in
let inv_f = Array.make (n + 1) 0 in
let () =
inv_f.(n) <- mod_inv f.(n) modulo;
for i = n - 1 downto 0 do
inv_f.(i) <- inv_f.(i + 1) * (i + 1) mod modulo
done in
(modulo, f, inv_f)
let fact n (_, f, _) = f.(n)
let inv_fact n (_, _, inv_f) = inv_f.(n)
let nPk n k ((mo, _, _) as c) =
if n < k then
0
else
fact n c * inv_fact (n - k) c mod mo
let nCk n k ((mo, _, _) as c) =
if n < k then
0
else
fact n c * inv_fact k c mod mo * inv_fact (n - k) c mod mo
let nHk n k c = if n = 0 && k = 0 then 1 else nCk (n + k - 1) k c
end
let id x = x
let n = Scanf.scanf "%d" id
let g = Array.make (n + 1) []
let () =
for i = 1 to n - 1 do
let (a, b) = Scanf.scanf " %d %d" (fun a b -> (a, b)) in
g.(a) <- b :: g.(a);
g.(b) <- a :: g.(b)
done
let rec dfs v p =
match g.(v) with
[w] when w = p -> 1 (* v *)
| _ -> List.fold_left (fun s w -> if w <> p then s + dfs w v else s) 0 g.(v)
let m = dfs 1 (-1)
let mo = 1_000_000_007
let c = Combination.init ~n:200100 ~modulo:mo
let cnt = if n >= 3 then
Combination.nCk (n - 1) (m - 1) c * Combination.nCk (n - 2) (m - 1) c mod mo * mod_inv m mo mod mo
else
1
let () =
print_int cnt;
print_newline ()
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