結果

問題 No.573 a^2[i] = a[i]
ユーザー tanzaku
提出日時 2017-10-06 23:22:05
言語 Rust
(1.83.0 + proconio)
結果
AC  
実行時間 15 ms / 2,000 ms
コード長 2,932 bytes
コンパイル時間 12,743 ms
コンパイル使用メモリ 377,416 KB
実行使用メモリ 5,248 KB
最終ジャッジ日時 2024-11-17 01:58:17
合計ジャッジ時間 13,532 ms
ジャッジサーバーID
（参考情報） 		judge2 / judge5
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ファイルパターン 結果
other AC * 47
権限があれば一括ダウンロードができます
コンパイルメッセージ
warning: fields `n` and `inv` are never read
  --> src/main.rs:8:5
   |
6  | struct Combination {
   |        ----------- fields in this struct
7  |     modular: usize,
8  |     n: usize,
   |     ^
9  |     fact: Vec<usize>,
10 |     inv: Vec<usize>,
   |     ^^^
   |
   = note: `Combination` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default

ソースコード

diff #
プレゼンテーションモードにする

#[allow(dead_code)]
const MOD: usize = 1_000000000 + 7;
#[derive(Debug)]
struct Combination {
    modular: usize,
    n: usize,
    fact: Vec<usize>,
    inv: Vec<usize>,
    invfact: Vec<usize>,
}
impl Combination {
    fn new(modular: usize, n: usize) -> Self {
        let mut fact = vec![0; n+1];
        let mut inv = vec![0; n+1];
        let mut invfact = vec![0; n+1];
        inv[1] = 1;
        fact[0] = 1;
        invfact[0] = 1;
        for i in 2..inv.len() {
            inv[i] = inv[modular % i] * (modular - modular / i) % modular;
        }
        for i in 1..inv.len() {
            fact[i] = i * fact[i-1] % modular;
            invfact[i] = inv[i] * invfact[i-1] % modular;
        }
        Combination {
            modular,
            n,
            fact,
            inv,
            invfact,
        }
    }
    fn comb(&self, n: usize, r: usize) -> usize {
        self.fact[n] * self.invfact[n-r] % self.modular * self.invfact[r] % self.modular
    }
}
fn modpow(n: usize, r: usize) -> usize {
    if r == 0 { return 1; }
    if r == 1 { return n; }
    let x = modpow(n, r / 2);
    if r % 2 == 0 {
        x * x % MOD
    } else {
        x * x % MOD * n % MOD
    }
}
fn main() {
    let mut cin = Scanner::new();
    // Σ C(n,i)*i^(n-i)
    let n = cin.next_usize();
    let c = Combination::new(MOD, n+1);
    let mut ans = 0;
    for i in 1..(n+1) {
        // println!("{} {} {}", i, c.comb(n, i), modpow(i, n-i));
        ans += c.comb(n, i) * modpow(i, n-i) % MOD;
    }
    println!("{}", ans % MOD);
}
struct Scanner {
    reader: std::io::Stdin,
    tokens: std::collections::VecDeque<String>,
}
impl Scanner {
    fn new() -> Self {
        Scanner {
            reader: std::io::stdin(),
            tokens: std::collections::VecDeque::new(),
        }
    }
    fn next(&mut self) -> String {
        if self.tokens.is_empty() {
            let mut s = String::new();
            loop {
                self.reader.read_line(&mut s).ok();
                let s = s.trim();
                if s.len() != 0 {
                    for it in s.split_whitespace() {
                        self.tokens.push_back(it.into())
                    }
                    break;
                }
            }
        }
        self.tokens.pop_front().unwrap()
    }
    fn next_generics<T>(&mut self) -> T where
        T: std::str::FromStr + std::marker::Copy,
        <T as std::str::FromStr>::Err: std::fmt::Debug
    {
        self.next().parse().unwrap()
    }
    
    #[allow(dead_code)] fn next_i32(&mut self) -> i32 { self.next_generics::<i32>() }
    #[allow(dead_code)] fn next_i64(&mut self) -> i64 { self.next_generics::<i64>() }
    #[allow(dead_code)] fn next_u64(&mut self) -> u64 { self.next_generics::<u64>() }
    #[allow(dead_code)] fn next_usize(&mut self) -> usize { self.next_generics::<usize>() }
    #[allow(dead_code)] fn next_isize(&mut self) -> isize { self.next_generics::<isize>() }
}
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