无序字母对——我其实一直都不会写欧拉回路吗

 1 #include<iostream>
 2 #include<vector>
 3 #include<cctype>
 4 #include<cstdio>
 5 #include<queue>
 6 using namespace std;
 7 const int N=64,INF=0x7fffffff;
 8 int n,cnt,pl=INF,pr=INF,dgr[N];
 9 bool ex[N],gr[N][N];
10 vector<int> res;
11 int encode(char x){
12     if(islower(x))return x-‘a‘+26;
13     else return x-‘A‘;
14 }
15 char uncode(int x){
16     if(x>25)return (char)(x+‘a‘-26);
17     else return (char)(x+‘A‘);
18 }
19 void dfs(int x){
20     for(int i=0;i<N;i++)
21         if(gr[x][i]){
22             gr[x][i]=gr[i][x]=false;
23             dfs(i);
24             res.push_back(i);
25         }
26 }
27 int main(){
28     cin>>n;
29     for(int i=1;i<=n;i++){
30         char t1,t2;cin>>t1>>t2;
31         int x=encode(t1),y=encode(t2);
32         ex[x]=ex[y]=gr[x][y]=gr[y][x]=true;
33         dgr[x]++;dgr[y]++;
34     }
35     for(int i=0;i<N;i++)
36         if(ex[i]&&dgr[i]%2)
37             cnt++,pl=min(pl,i);
38         else if(ex[i]&&dgr[i])pr=min(pr,i);
39     if(cnt!=0&&cnt!=2)cout<<"No Solution"<<endl;
40     else{
41         int p=cnt?pl:pr;
42         dfs(p);
43         res.push_back(p);
44         for(int i=res.size()-1;i>=0;i--)cout<<uncode(res[i]);
45         cout<<endl;
46     }
47     return 0;
48 }