POJ 2337 欧拉回路

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
char s[1005][25];
int first[60],next[1005],tot,top,v[1005];
int cases,n,ansx,ansy,ansz,in[26],out[26],ans[1005];
bool vis[1005],flag,VIS[26];
struct node{char str[25];int length;}edge[1005];
void add(int x,int y,int z){v[z]=y;next[z]=first[x];first[x]=z;}
bool cmp(node x,node y){return strcmp(x.str,y.str)>0?0:1;}
void dfs(int x){
for(int i=first[x];~i;i=next[i])
if(!vis[i]){
VIS[v[i]]=1;
vis[i]=1,dfs(v[i]);
ans[++top]=i;
}
}
int main(){
scanf("%d",&cases);
while(cases--){
memset(first,-1,sizeof(first));
memset(in,0,sizeof(in));
memset(out,0,sizeof(out));
memset(vis,0,sizeof(vis));
memset(VIS,0,sizeof(VIS));
flag=ansx=ansy=ansz=top=0;
scanf("%d",&n);
for(int i=1;i<=n;i++){
scanf("%s",edge[i].str);
edge[i].length=strlen(edge[i].str);
out[edge[i].str[0]-'a']++;
in[edge[i].str[edge[i].length-1]-'a']++;
}
sort(edge+1,edge+1+n,cmp);
for(int i=n;i;i--)
add(edge[i].str[0]-'a',edge[i].str[edge[i].length-1]-'a',i);
for(int i=0;i<=25;i++){
if(in[i]-out[i]==1)ansx++;
else if(out[i]-in[i]==1)ansy++;
else if(in[i]!=out[i])ansz++;
}
if(!ansz&&ansx==ansy&&(ansx==0||ansx==1)){
int jy;
if(ansx==1){
for(int i=0;i<26;i++)
if(out[i]-in[i]==1){jy=i;break;}
}
else{
for(int i=0;i<26;i++)
if(out[i]){jy=i;break;}
}
VIS[jy]=1;
dfs(jy);
for(int i=0;i<=25;i++)
if((in[i]||out[i])&&!VIS[i])flag=1;
}
else flag=1;
if(!flag){
for(int i=top;i>=2;i--)
printf("%s.",edge[ans[i]].str);
printf("%s\n",edge[ans[1]].str);
}
else puts("***");
}
}