hdu5651 题解

链接:hdu5651

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#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
#define rep(i,x,y) for(register int i=x;i<=y;++i)
#define repd(i,x,y) for(register int i=x;i>=y;--i)
#define ll long long
using namespace std;
const int N=1e5;
const ll p=1000000007;
char str[N];
int a[30],T,len,cnt,flag;

int (ll a,ll b,ll &d,ll &x,ll &y){
if(b==0){x=1; y=0; d=a;}
else {exgcd(b,a%b,d,x,y); ll t=x;x=y;y=t-a/b*x;}
}

ll inv(ll a,ll p){
ll d,x,y;
exgcd(a,p,d,x,y);
return d==1?(x%p+p)%p:-1;
}
void readin(){
cin>>str;
len=strlen(str);cnt=flag=0;
memset(a,0,sizeof(a));
rep(i,0,len-1)a[str[i]-'a']++;
rep(i,0,29){
if(a[i]&1)flag++;
if(a[i]){
a[i]>>=1;
cnt+=a[i];
}
}
}

ll sum(ll X){
ll tp=1;
rep(i,2,X)tp=tp*i%p;
return tp;
}

int main(){
ios::sync_with_stdio(false);
cin>>T;
while(T--){
readin();
if(flag>1){
cout<<0<<endl;
continue;
}
rep(i,0,26)if(a[i]!=0){
a[i]=sum(a[i]);
a[i]=inv(a[i],p);
}
ll ans=sum(cnt);
rep(i,0,26)if(a[i])ans=ans*a[i]%p;
cout<<ans<<endl;
}
return 0;
}