Submission #3411336

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Source Code Expand

/// Thank you tanakh!!!
/// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let mut s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

const MOD: usize = 998244353;

fn main() {
    input!(n: usize, a: usize, b: usize, k: usize);

    let mut candidates = vec![];
    for x in 0..(n + 1) {
        if a * x > k {
            break;
        }
        let rest = k - a * x;
        if rest % b != 0 {
            continue;
        }
        let y = rest / b;
        if y > n {
            continue;
        }
        candidates.push((x, y));
    }

    let combination = Combination::new(n + 1, MOD);
    let mut ans = 0;
    for &(x, y) in candidates.iter() {
        let x = combination.get(n, x);
        let y = combination.get(n, y);
        ans = (ans + (x * y) % MOD) % MOD;
    }
    println!("{}", ans);
}

pub struct Combination {
    fact: Vec<usize>,
    inv_fact: Vec<usize>,
    modulo: usize,
}

impl Combination {
    pub fn new(max: usize, modulo: usize) -> Combination {
        let mut inv = vec![0; max + 1];
        let mut fact = vec![0; max + 1];
        let mut inv_fact = vec![0; max + 1];
        inv[1] = 1;
        for i in 2..(max + 1) {
            inv[i] = inv[modulo % i] * (modulo - modulo / i) % modulo;
        }
        fact[0] = 1;
        inv_fact[0] = 1;
        for i in 0..max {
            fact[i + 1] = fact[i] * (i + 1) % modulo;
        }
        for i in 0..max {
            inv_fact[i + 1] = inv_fact[i] * inv[i + 1] % modulo;
        }
        Combination {
            fact: fact,
            inv_fact: inv_fact,
            modulo: modulo,
        }
    }

    pub fn get(&self, x: usize, y: usize) -> usize {
        assert!(x >= y);
        self.fact[x] * self.inv_fact[y] % self.modulo * self.inv_fact[x - y] % self.modulo
    }
}

Submission Info

Compile Error

warning: variable does not need to be mutable, #[warn(unused_mut)] on by default
  --> ./Main.rs:9:13
   |
9  |         let mut s = {
   |             ^^^^^
...
55 |     input!(n: usize, a: usize, b: usize, k: usize);
   |     ----------------------------------------------- in this macro invocation

Judge Result