Submission #36300737

Source Code Expand

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#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=20000005,mod=998244353;
ll qpow(ll n,int k){
  ll ans=1;
  while(k){
    if(k&1)ans=ans*n%mod;
    n=n*n%mod;
    k>>=1;
  }
  return ans;
}
int n,m; 
ll fac[N],ifac[N];
ll C(int x,int y){
  if(x<0||y<0||x<y)return 0;
  return fac[x]*ifac[y]%mod*ifac[x-y]%mod;
}
int main(){
    cin.tie(0);cout.tie(0);
 
 
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#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=20000005,mod=998244353;
ll qpow(ll n,int k){
	ll ans=1;
	while(k){
		if(k&1)ans=ans*n%mod;
		n=n*n%mod;
		k>>=1;
	}
	return ans;
}
int n,m; 
ll fac[N],ifac[N];
ll C(int x,int y){
	if(x<0||y<0||x<y)return 0;
	return fac[x]*ifac[y]%mod*ifac[x-y]%mod;
}
int main(){
    cin.tie(0);cout.tie(0);
	ios::sync_with_stdio(0);
	fac[0]=1;
	for(int i=1;i<=20000000;i++)fac[i]=fac[i-1]*i%mod;
	ifac[20000000]=qpow(fac[20000000],mod-2);
	for(int i=20000000;i>=1;i--)ifac[i-1]=ifac[i]*i%mod;
	cin>>n>>m;
	ll ans=0;
	for(int t=0;t<3;t++){
		if(t>m)break;
		for(int i=0;i<=n-1;i++){
			int an=t+i+2*(n-1-i);
			if(an>m)continue;
			int f=(m-an)/3;
			ans=(ans+C(n+f,n)*C(n-1,i)%mod)%mod;
		}
	}
	cout<<ans<<"\n";
	return 0;
}

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