Problem:
Score : 500 points

Problem Statement

There are N blocks arranged in a row. Let us paint these blocks.

We will consider two ways to paint the blocks different if and only if there is a block painted in different colors in those two ways.

Find the number of ways to paint the blocks under the following conditions:

For each block, use one of the M colors, Color 1 through Color M, to paint it. It is not mandatory to use all the colors.

There may be at most K pairs of adjacent blocks that are painted in the same color.

Since the count may be enormous, print it modulo 998244353.

Constraints

All values in input are integers.

1 \leq N, M \leq 2 \times 10^5

0 \leq K \leq N - 1

Input

Input is given from Standard Input in the following format:

N M K

Output

Print the answer.

Sample Input 1

3 2 1

Sample Output 1

6

The following ways to paint the blocks satisfy the conditions: 112, 121, 122, 211, 212, and 221. Here, digits represent the colors of the blocks.

Sample Input 2

100 100 0

Sample Output 2

73074801

Sample Input 3

60522 114575 7559

Sample Output 3

479519525

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

#![allow(unused, non_snake_case, dead_code, non_upper_case_globals)]
#![macro_use]

use std::cmp::*;
use std::collections::*;
use std::io::*;
use std::mem::*;
use std::num::*;
use std::slice::*;

const MOD: usize = 998244353;
fn main() {
    let mut io = IO::new(stdin(), stdout(), stderr());
    // ===================================== //
    let (n, m, k): (i64, i64, i64) = (io.read(), io.read(), io.read());
    let mut md = ModComb::new((n + 111111) as usize, 998244353);
    let mut ans = 0;
    for ks in 0..k + 1 {
        let nn = n - ks;
        let mut tmp = 0;
        tmp = md.nCk(n - 1, ks) * m % md.p;
        //io.debug(tmp);
        // io.debug(md.nCk(5, 2));
        tmp *= modpow(m - 1, nn - 1, md.p);
        tmp %= md.p;
        //io.debug(tmp);
        ans += tmp;
        ans %= md.p;
    }
    io.writeln(ans % md.p);
}

// IO
struct IO<R: Read, W: Write, E: Write> {
    Read: R,
    Write: BufWriter<W>,
    Error: BufWriter<E>,
}
impl<R: Read, W: Write, E: Write> IO<R, W, E> {
    fn new(r: R, w: W, e: E) -> IO<R, W, E> {
        IO {
            Read: r,
            Write: BufWriter::new(w),
            Error: BufWriter::new(e),
        }
    }
    fn read<T>(&mut self) -> T
    where
        T: std::str::FromStr,
    {
        let next: String = self
            .Read
            .by_ref()
            .bytes()
            .map(|c| c.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect();
        next.parse().ok().unwrap()
    }
    fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
    fn readn<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read::<T>()).collect::<Vec<_>>()
    }
    fn readmat<T: std::str::FromStr>(&mut self, n: usize, m: usize) -> Vec<Vec<T>> {
        (0..n).map(|_| self.readn(m)).collect()
    }
    fn write<S: ToString>(&mut self, val: S) {
        self.Write.write(val.to_string().as_bytes());
    }
    fn writeln<S: ToString>(&mut self, val: S) {
        self.Write.write(val.to_string().as_bytes());
        self.Write.write(b"\n");
    }
    fn debug<S: std::fmt::Debug>(&mut self, val: S) {
        writeln!(self.Error, "(debug) {:?}", &val);
    }
}

struct ModComb {
    fact: Vec<i64>,
    fact_inv: Vec<i64>,
    n: usize,
    p: i64,
}
fn modpow(x: i64, n: i64, m: i64) -> i64 {
    let mut res = 1;
    let mut x = x % m;
    let mut n = n;
    while n > 0 {
        if n & 1 == 1 {
            res = (res * x) % m;
        }
        x = (x * x) % m;
        n >>= 1;
    }
    res
}
impl ModComb {
    fn initialize(&mut self) {
        let n = self.n;

        self.fact[0] = 1;
        for i in 1..n {
            self.fact[i] = (self.fact[i - 1] * i as i64) % self.p;
        }
        self.fact_inv[n - 1] = modpow(self.fact[n - 1], self.p - 2, self.p);
        for i in (0..n - 1).rev() {
            self.fact_inv[i] = (self.fact_inv[i + 1] * (i + 1) as i64) % self.p;
        }
    }
    fn new(max_n: usize, p: i64) -> ModComb {
        let mut ft = ModComb {
            fact: vec![0; max_n + 1],
            fact_inv: vec![0; max_n + 1],
            n: max_n + 1,
            p: p,
        };
        ModComb::initialize(&mut ft);
        ft
    }
    fn fact(&self, n: usize) -> i64 {
        self.fact[n]
    }
    fn nCk(&self, n: i64, k: i64) -> i64 {
        if n < k {
            return 0;
        }
        (self.nPk(n, k) * self.fact_inv[k as usize]) % self.p
    }
    fn nPk(&self, n: i64, k: i64) -> i64 {
        if n < k {
            return 0;
        }
        self.fact[n as usize] * self.fact_inv[(n - k) as usize] % self.p
    }
    fn nHk(&self, n: i64, k: i64) -> i64 {
        if n == 0 && k == 0 {
            return 1;
        }
        self.nCk(n + k - 1, k)
    }
    fn nSk(&self, n: i64, k: i64) -> i64 {
        if n < k {
            return 0;
        }
        let mut res = 0;
        for i in 0..k + 1 {
            let v = self.nCk(k, i) * modpow(i, n, self.p) % self.p;
            if (k - i) % 2 == 1 {
                // odd
                res = (res + self.p - v) % self.p;
            } else {
                //
                res = (res + v) % self.p;
            }
        }
        return res * self.fact_inv[k as usize] % self.p;
    }
}