提出 #22119383

---

ソースコード 拡げる

use std::time::Instant;

fn main() {
    let (r, w) = (std::io::stdin(), std::io::stdout());
    let mut sc = IO::new(r.lock(), w.lock());
    let n: usize = sc.read();
    let m: usize = sc.read();
    let k: usize = sc.read();

    let mut no = vec![vec![false; n]; n];
    for _ in 0..m {
        let a: usize = sc.read();
        let b: usize = sc.read();
        no[a][b] = true;
        no[b][a] = true;

        assert!(a < b);
    }

    let start = Instant::now();

    let mut ok = 0;
    let mut ng = 0;
    let mut rng_state = 717;
    loop {
        if start.elapsed().as_millis() > 3000 {
            break;
        }
        let mut p = (0..n).collect::<Vec<_>>();
        for _ in 0..k {
            let i = xor_shift_64(&mut rng_state) % n;
            let mut j = xor_shift_64(&mut rng_state) % (n - 1);
            if i <= j {
                j += 1;
            }
            p.swap(i, j);
        }
        let is_ok = (0..n).all(|i| !no[p[i]][p[(i + 1) % n]]);

        if is_ok {
            ok += 1;
        } else {
            ng += 1;
        }
    }

    println!("{}", ok as f64 / (ok + ng) as f64);
}

fn xor_shift_64(state: &mut usize) -> usize {
    let mut x = *state;
    x ^= x << 13;
    x ^= x >> 7;
    x ^= x << 17;
    *state = x;
    x
}

pub trait NextPermutation {
    fn next_permutation(&mut self) -> bool;
}

impl<T> NextPermutation for [T]
where
    T: PartialOrd,
{
    fn next_permutation(&mut self) -> bool {
        if self.len() < 2 {
            return false;
        }

        let mut i = self.len() - 1;
        while i > 0 && self[i - 1] >= self[i] {
            i -= 1;
        }

        if i == 0 {
            return false;
        }

        let mut j = self.len() - 1;
        while j >= i && self[j] <= self[i - 1] {
            j -= 1;
        }

        self.swap(j, i - 1);
        self[i..].reverse();
        true
    }
}

pub struct IO<R, W: std::io::Write>(R, std::io::BufWriter<W>);

impl<R: std::io::Read, W: std::io::Write> IO<R, W> {
    pub fn new(r: R, w: W) -> IO<R, W> {
        IO(r, std::io::BufWriter::new(w))
    }
    pub fn write<S: ToString>(&mut self, s: S) {
        use std::io::Write;
        self.1.write_all(s.to_string().as_bytes()).unwrap();
    }
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .0
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r' && b != b'\t')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn usize0(&mut self) -> usize {
        self.read::<usize>() - 1
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }
    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}

提出情報

ジャッジ結果