Problem:
Score : 600 points

Problem Statement

We have a grid with A horizontal rows and B vertical columns, with the squares painted white. On this grid, we will repeatedly apply the following operation:

Assume that the grid currently has a horizontal rows and b vertical columns. Choose "vertical" or "horizontal".

If we choose "vertical", insert one row at the top of the grid, resulting in an (a+1) \times b grid.

If we choose "horizontal", insert one column at the right end of the grid, resulting in an a \times (b+1) grid.

Then, paint one of the added squares black, and the other squares white.

Assume the grid eventually has C horizontal rows and D vertical columns. Find the number of ways in which the squares can be painted in the end, modulo 998244353.

Constraints

1 \leq A \leq C \leq 3000

1 \leq B \leq D \leq 3000

A, B, C, and D are integers.

Input

Input is given from Standard Input in the following format:

A B C D

Output

Print the number of ways in which the squares can be painted in the end, modulo 998244353.

Sample Input 1

1 1 2 2

Sample Output 1

3

Any two of the three squares other than the bottom-left square can be painted black.

Sample Input 2

2 1 3 4

Sample Output 2

65

Sample Input 3

31 41 59 265

Sample Output 3

387222020

Solution in Rust (1.42.0) (judge verdict: Accepted)

use crate::mod_int::ModInt;
use std::cmp::{max, min};

const MOD: u64 = 998244353;

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

    let sx: usize = sc.read();
    let sy: usize = sc.read();
    let tx: usize = sc.read();
    let ty: usize = sc.read();
    if sx == tx && sy == ty {
        println!("1");
        return;
    }

    let inv2 = m(1) / 2;
    let mut dp = vec![vec![m(0); ty + 1]; tx + 1];
    dp[sx][sy] = m(1);
    for x in (sx + 1)..=tx {
        dp[x][sy] = dp[x - 1][sy] * (sy as u64);
    }
    for y in (sy + 1)..=ty {
        dp[sx][y] = dp[sx][y - 1] * (sx as u64);
    }

    for to_sum in (sx + sy + 2)..=(tx + ty) {
        let x_from = max(to_sum, sx + ty) - ty;
        let x_to = min(tx, to_sum - sy);
        for x in x_from..=x_to {
            let y = to_sum - x;
            if x == sx || y == sy {
                continue;
            }

            let t1 = dp[x - 1][y] * (y as u64);
            let t2 = dp[x][y - 1] * (x as u64);
            let t3 = dp[x - 1][y - 1] * (x as u64 - 1) * (y as u64 - 1);
            dp[x][y] = t1 + t2 - t3;
        }
    }

    println!("{}", dp[tx][ty].v);
}

fn m(v: u64) -> ModInt<u64> {
    ModInt::new(v, MOD)
}

pub mod mod_int {
    use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Rem, Sub, SubAssign};

    pub struct ModInt<T> {
        pub v: T,
        pub modulo: T,
    }

    impl<T> Copy for ModInt<T> where T: Copy {}
    impl<T> Clone for ModInt<T>
    where
        T: Copy,
    {
        fn clone(&self) -> Self {
            ModInt {
                v: self.v,
                modulo: self.modulo,
            }
        }
    }

    impl<T> Add<T> for ModInt<T>
    where
        T: Add<Output = T> + Sub<Output = T> + Rem<Output = T> + Copy + PartialOrd,
    {
        type Output = ModInt<T>;
        fn add(self, mut rhs: T) -> ModInt<T> {
            if rhs >= self.modulo {
                rhs = rhs % self.modulo;
            }
            let mut t = rhs + self.v;
            if t >= self.modulo {
                t = t - self.modulo;
            }
            ModInt {
                v: t,
                modulo: self.modulo,
            }
        }
    }

    impl<T> Add<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Add<T, Output = ModInt<T>>,
    {
        type Output = ModInt<T>;
        fn add(self, rhs: ModInt<T>) -> ModInt<T> {
            self + rhs.v
        }
    }

    impl<T> Sub<T> for ModInt<T>
    where
        T: Add<Output = T> + Sub<Output = T> + Rem<Output = T> + Copy + PartialOrd,
    {
        type Output = ModInt<T>;
        fn sub(self, rhs: T) -> ModInt<T> {
            let rhs = if rhs >= self.modulo {
                rhs % self.modulo
            } else {
                rhs
            };
            let value = if self.v < rhs {
                self.v + self.modulo
            } else {
                self.v
            };
            ModInt {
                v: value - rhs,
                modulo: self.modulo,
            }
        }
    }

    impl<T> Sub<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Sub<T, Output = ModInt<T>>,
    {
        type Output = ModInt<T>;
        fn sub(self, rhs: ModInt<T>) -> ModInt<T> {
            self - rhs.v
        }
    }

    impl<T> AddAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Add<T, Output = ModInt<T>>,
    {
        fn add_assign(&mut self, other: T) {
            *self = *self + other;
        }
    }
    impl<T> AddAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Add<ModInt<T>, Output = ModInt<T>>,
    {
        fn add_assign(&mut self, other: ModInt<T>) {
            *self = *self + other;
        }
    }

    impl<T> SubAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Sub<T, Output = ModInt<T>>,
    {
        fn sub_assign(&mut self, other: T) {
            *self = *self - other;
        }
    }

    impl<T> SubAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Sub<ModInt<T>, Output = ModInt<T>>,
    {
        fn sub_assign(&mut self, other: ModInt<T>) {
            *self = *self - other;
        }
    }

    impl<T> Div<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Div<T, Output = ModInt<T>>,
    {
        type Output = ModInt<T>;
        fn div(self, rhs: ModInt<T>) -> ModInt<T> {
            self / rhs.v
        }
    }

    impl<T> DivAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Div<T, Output = ModInt<T>>,
    {
        fn div_assign(&mut self, rhs: T) {
            *self = *self / rhs
        }
    }
    impl<T> DivAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Div<ModInt<T>, Output = ModInt<T>>,
    {
        fn div_assign(&mut self, rhs: ModInt<T>) {
            *self = *self / rhs
        }
    }

    impl<T> Mul<T> for ModInt<T>
    where
        T: Mul<Output = T> + Rem<Output = T> + Copy + PartialOrd,
    {
        type Output = ModInt<T>;

        fn mul(self, mut rhs: T) -> ModInt<T> {
            if rhs >= self.modulo {
                rhs = rhs % self.modulo;
            }
            let t = (self.v * rhs) % self.modulo;
            ModInt {
                v: t,
                modulo: self.modulo,
            }
        }
    }
    impl<T> Mul<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<T, Output = ModInt<T>>,
    {
        type Output = ModInt<T>;
        fn mul(self, rhs: ModInt<T>) -> ModInt<T> {
            self * rhs.v
        }
    }

    impl<T> MulAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<T, Output = ModInt<T>>,
    {
        fn mul_assign(&mut self, rhs: T) {
            *self = *self * rhs;
        }
    }

    impl<T> MulAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<ModInt<T>, Output = ModInt<T>>,
    {
        fn mul_assign(&mut self, rhs: ModInt<T>) {
            *self = *self * rhs;
        }
    }

    impl<T> ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<ModInt<T>, Output = ModInt<T>>,
    {
        pub fn general_pow(self, e: u64, one: ModInt<T>) -> ModInt<T> {
            let mut result = one;
            let mut cur = self;
            let mut e = e;
            while e > 0 {
                if e & 1 == 1 {
                    result *= cur;
                }
                e >>= 1;
                cur *= cur;
            }
            result
        }
    }

    impl Div<u64> for ModInt<u64> {
        type Output = ModInt<u64>;
        fn div(self, mut rhs: u64) -> ModInt<u64> {
            if rhs >= self.modulo {
                rhs %= self.modulo;
            }
            self * ModInt {
                v: rhs,
                modulo: self.modulo,
            }
            .pow(self.modulo - 2)
        }
    }

    impl ModInt<u64> {
        pub fn new(v: u64, modulo: u64) -> Self {
            Self {
                v: v % modulo,
                modulo,
            }
        }

        pub fn pow(self, e: u64) -> ModInt<u64> {
            self.general_pow(e, ModInt::new(1, self.modulo))
        }
    }
}

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) -> Self {
        Self(r, std::io::BufWriter::new(w))
    }
    pub fn write<S: ToString>(&mut self, s: S) {
        use std::io::Write;
        self.1.write(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 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()
    }
}