题目链接：http://poj.org/problem?id=2337

题意：给定一些单词，假设一个单词的尾字母与还有一个的首字母同样则能够连接。问能否够每一个单词用一次，将全部单词连接，能够则输出字典序最小的序列。

代码：
（bin 神的板子）

#include <stdio.h>
#include <ctime>
#include <math.h>
#include <limits.h>
#include <complex>
#include <string>
#include <functional>
#include <iterator>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <list>
#include <bitset>
#include <sstream>
#include <iomanip>
#include <fstream>
#include <iostream>
#include <ctime>
#include <cmath>
#include <cstring>
#include <cstdio>
#include <time.h>
#include <ctype.h>
#include <string.h>
#include <assert.h>using namespace std;int t;
int n;
string s[1010];struct Edge
{int to, next;int index;bool flag;
}edge[2010];int head[300], tot;void init()
{tot = 0;memset(head,-1,sizeof(head));
}void addedge(int u, int v, int index)
{edge[tot].to = v;edge[tot].next = head[u];edge[tot].index = index;edge[tot].flag = false;head[u] = tot++;
}int in[250], out[250];int cnt;
int ans[1010];void dfs(int u)
{for (int i = head[u]; i != -1; i = edge[i].next){if (!edge[i].flag){edge[i].flag = true;dfs(edge[i].to);ans[cnt++] = edge[i].index;}}
}int main()
{int t;cin >> t;while (t--){scanf("%d",&n);for (int i = 0; i < n; i++)cin >> s[i];sort(s, s + n);init();memset(in,0,sizeof(in));memset(out, 0, sizeof(out));int start = 100;for (int i = n - 1; i >= 0; i--){int u = s[i][0] - 'a';int v = s[i][s[i].length() - 1] - 'a';addedge(u,v,i);out[u]++;in[v]++;if (u < start) start = u;if (v < start) start = v;}int cc1 = 0, cc2 = 0;for (int i = 0; i < 26; i++){if (out[i] - in[i] == 1){cc1++;start = i;}else if (out[i] - in[i] == -1)cc2++;else if (out[i] - in[i] != 0)cc1 = 3;}if (!((cc1 == 0 && cc2 == 0) || (cc1 == 1 && cc2 == 1))){printf("***\n");continue;}cnt = 0;dfs(start);if (cnt != n){printf("***\n");continue;}for (int i = n-1; i >=0 ; i--){cout << s[ans[i]];if (i != 0) printf(".");else printf("\n");}}return 0;
}