https://www.luogu.org/problemnew/show/P1341

题解：

参考文章：https://blog.csdn.net/weixin_43272781/article/details/88553573

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=128+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
int ans,cnt,flag,temp,sum;
bool a[N][N];
bool vis[N];
int deg[N];
char str1,str2;
char ANS[N];
void dfs(int rt){
    for(int i='A';i<='z';i++){
        if(a[rt][i]){
            a[rt][i]=a[i][rt]=0;
            dfs(i);
        }
    }
    ANS[n-ans++]=rt;
}

int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    //scanf("%d",&t);
    //while(t--){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        cin>>str1>>str2;
        a[str1][str2]=a[str2][str1]=1;
        deg[str1]++;
        deg[str2]++;
    }
    int h=0;
    for(int i='A';i<='z';i++){
        if(deg[i]&1){
            cnt++;
            if(!h)h=i;
        }
    }
    if(!h)
        for(int i='A';i<='z';i++){
            if(deg[i]){
                h=i;
                break;
            }
        }
    if(cnt&&cnt!=2){
        cout<<"No Solution";
        return 0;
    }
    dfs(h);
    if(ans<n+1){
        cout<<"No Solution";
        return 0;
    }
    ANS[n+1]='\0';
    cout<<ANS<<endl;
    //}

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}