結果

問題 No.3028 No.9999
ユーザー atcoder8
提出日時 2025-02-21 22:39:28
言語 Rust
(1.83.0 + proconio)
結果
AC  
実行時間 2 ms / 4,000 ms
コード長 2,109 bytes
コンパイル時間 16,508 ms
コンパイル使用メモリ 393,696 KB
実行使用メモリ 6,820 KB
最終ジャッジ日時 2025-02-21 22:39:46
合計ジャッジ時間 14,640 ms
ジャッジサーバーID
（参考情報） 		judge5 / judge1
このコードへのチャレンジ
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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

use proconio::input;
fn main() {
    input! {
        n: usize,
    }
    println!("{}", solve(n));
}
fn solve(n: usize) -> usize {
    if n == 1 {
        return 1;
    }
    let factors = prime_factorization(n);
    let carmichael = factors.iter().fold(1_usize, |lcm, &(p, e)| {
        calc_lcm(lcm, p.pow(e as u32 - 1) * (p - 1))
    });
    *find_divisors(carmichael)
        .iter()
        .find(|&&d| pow_mod(10, d, n) == 1)
        .unwrap()
}
/// Creates a sequence consisting of the divisors of `n`.
pub fn find_divisors(n: usize) -> Vec<usize> {
    assert_ne!(n, 0, "`n` must be at least 1.");
    let mut divisors = vec![];
    for i in (1..).take_while(|&i| i <= n / i) {
        if n % i == 0 {
            divisors.push(i);
            if n / i != i {
                divisors.push(n / i);
            }
        }
    }
    divisors.sort_unstable();
    divisors
}
/// Performs prime factorization of `n`.
///
/// The result of the prime factorization is returned as a
/// list of prime factor and exponent pairs.
pub fn prime_factorization(n: usize) -> Vec<(usize, usize)> {
    assert_ne!(n, 0, "`n` must be at least 1.");
    let mut factors = vec![];
    let mut t = n;
    for p in 2.. {
        if p * p > t {
            break;
        }
        let mut e = 0;
        while t % p == 0 {
            t /= p;
            e += 1;
        }
        if e != 0 {
            factors.push((p, e));
        }
    }
    if t != 1 {
        factors.push((t, 1));
    }
    factors
}
/// Calculate the remainder of `exp` power of `base` divided by `m`.
pub fn pow_mod(base: usize, exp: usize, m: usize) -> usize {
    let mut ret = 1 % m;
    let mut mul = base % m;
    let mut t = exp;
    while t != 0 {
        if t & 1 == 1 {
            ret = ret * mul % m;
        }
        mul = mul * mul % m;
        t >>= 1;
    }
    ret
}
fn calc_gcd(a: usize, b: usize) -> usize {
    let (mut a, mut b) = (a, b);
    while b != 0 {
        let r = a % b;
        a = b;
        b = r;
    }
    a
}
fn calc_lcm(a: usize, b: usize) -> usize {
    a / calc_gcd(a, b) * b
}
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