10082. 「一本通 3.3 例 1」Word Rings

#include<algorithm>
#include<bitset>
#include<complex>
#include<deque>
#include<exception>
#include<fstream>
#include<functional>
#include<iomanip>
#include<ios>
#include<iosfwd>
#include<iostream>
#include<istream>
#include<iterator>
#include<limits>
#include<list>
#include<locale>
#include<map>
#include<memory>
#include<new>
#include<numeric>
#include<ostream>
#include<queue>
#include<set>
#include<sstream>
#include<stack>
#include<stdexcept>
#include<streambuf>
#include<string>
#include<typeinfo>
#include<utility>
#include<valarray>
#include<vector>
#include<cctype>
#include<cerrno>
#include<cfloat>
#include<ciso646>
#include<climits>
#include<clocale>
#include<cmath>
#include<csetjmp>
#include<csignal>
#include<cstdarg>
#include<cstddef>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#define E 200010
#define eps 1e-3
using namespace std;
inline int read(){
    int res=0,f=1;char ch=getchar();
    while(ch<'0'ch>'9'){if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9') res=res*10+ch-'0',ch=getchar();
    return res*f;
}
inline void write(int x){
    if(x<0) putchar('-'),x=-x;
    if(x<10) putchar(x+'0');
    else{
        write(x/10);
        putchar(x%10+'0');
    }
}
//queue<int> q;
//set<int> s;
//priority_queue<int> q1;
//priority_queue<int,vector<int>,greater<int> > q2;
//list<int> l;
//stack<int> s;
int n;
string str[100010];
int fir[E],nxt[E],son[E],tot,cnt,Max;
double w[E],dis[E],flag;
int vis[E];
int f[6666];
void add(int x,int y,double z){++tot;son[tot]=y;nxt[tot]=fir[x];fir[x]=tot;w[tot]=z;}
void spfa(int s,int v,double mid){
    if(flag==1) return ;
    vis[s]=v;
    for(int i=fir[s];i;i=nxt[i]){
        int to=son[i];
        if(dis[s]+w[i]>dis[to]+mid){
            dis[to]=dis[s]+w[i]-mid;
            if(dis[to]>Max){
                flag=1;
                return ;
            }
            if(!vis[to]) spfa(to,v,mid);
            if(flag) return ;
            else if(vis[to]==v){
                flag=1;
                return ;
            }
        }
    }
    vis[s]=0;
}
bool check(double mid){
    flag=0;
    for(int i=0;i<=cnt;i++) dis[i]=0.0;
    memset(vis,0,sizeof(vis));
    for(int i=1;i<=cnt;i++){
        spfa(i,i,mid);
        if(flag==1) break;
    }
    return flag;
}
int main(){
//    freopen("code.in","r",stdin);freopen("code.out","w",stdout);
    n=read();
    while(n!=0){
        for(int i=1;i<=n;i++) cin>>str[i];
        memset(fir,0,sizeof(fir));
        memset(f,0,sizeof(f));
        tot=0;cnt=0;Max=0;
        for(int i=1;i<=n;i++){
            int len=str[i].length();
            Max=max(Max,len);
            int a=(str[i][0]-'a')*26+str[i][1]-'a';
            int b=(str[i][len-2]-'a')*26+str[i][len-1]-'a';
            if(!f[a]) f[a]=++cnt;
            int A=f[a];
            if(!f[b]) f[b]=++cnt;
            int B=f[b];
            add(A,B,(double)len);
        }
        Max*=n;
        double l=0,r=1000,ans=-1,mid;
        while(l+eps<r){
            mid=(l+r)/2;
            if(check(mid)) l=mid,ans=mid;
            else r=mid;
        }
        if(ans!=-1) printf("%.2lf\n",ans);
        else puts("No solution");
        n=read();
    }
    return 0;
}