Submission #34618748

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Source Code Expand

#include<bits/stdc++.h>
#define LL long long
#define pb push_back
#define SZ(x) ((int)x.size()-1)
#define ms(a,b) memset(a,b,sizeof a)
#define F(i,a,b) for (int i=(a);i<=(b);++i)
#define DF(i,a,b) for (int i=(a);i>=(b);--i)
//#define mp make_pair
//#define OO(x) fixed<<setprecision(x)
using namespace std;
//mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
inline int read(){
	char ch=getchar(); int w=1,c=0;
	for(;!isdigit(ch);ch=getchar()) if (ch=='-') w=-1;
	for(;isdigit(ch);ch=getchar()) c=(c<<1)+(c<<3)+(ch^48);
	return w*c;
}
const int mod=998244353;//?????????

LL fast(LL x,LL p){
	LL ret=1;
	for (;p;p>>=1,x=x*x%mod) if (p&1) ret=ret*x%mod;
	return ret;
}
const int M=1e6+10;
LL fac[M],inv[M],iv[M];
void init(int n){
	fac[0]=1;
	F(i,1,n) fac[i]=fac[i-1]*i%mod;
	inv[n]=fast(fac[n],mod-2);
	DF(i,n,1) inv[i-1]=inv[i]*i%mod;
	iv[1]=1;
	F(i,2,n) iv[i]=(mod-mod/i)*iv[mod%i]%mod;
}
LL C(int x,int y){
	if (y<0 || x<y) return 0;
	return fac[x]*inv[y]%mod*inv[x-y]%mod;
}
int n,m;
int main(){
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	n=read(); m=read();
	init(1000000);
	cout<<fast(m,n-1)*fast(n,m)%mod<<"\n";
//	LL o=1;
//	int nn=n-1;
//	LL ans=0;
//	F(i,0,m){
//		if (!o) continue;
//		LL tmp=0;
//		F(j,nn,nn){
//			tmp=(tmp+C(nn,j)*fast(2,j)%mod*inv[m-i-j]%mod*inv[i+j]%mod*fac[j])%mod;
//		}
//		ans=(ans+tmp*o%mod*fac[m])%mod;	
//		o=o*(1ll*nn*(nn-1)/2%mod)%mod;
//		nn-=2;
//	}
//	cout<<ans<<"\n";
	return 0;
}
/* stuff you should look for
	* int overflow, array bounds
	* special cases (n=1?)
	* do smth instead of nothing and stay organized
	* WRITE STUFF DOWN
	* DON'T GET STUCK ON ONE APPROACH
*/

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