1 #include <iostream>
  2 #include <algorithm>
  3 #include <cstring>
  4 #include <cstdio>
  5 #include <cmath>
  6 #include <stack>
  7 #include <set>
  8 #include <map>
  9 #include <queue>
 10 #include <climits>
 11 #include <bitset>
 12 #define eps 1e-6
 13 using namespace std;
 14 
 15 int in[30], out[30], my_book[1010], my_route[1010], n;
 16 
 17 struct node
 18 {
 19     int h, t;
 20     char s[35];
 21 }my_str[1010];
 22 
 23 bool cmp(node a, node b)
 24 {
 25     return strcmp(a.s, b.s) < 0;
 26 }
 27 
 28 int euler()
 29 {
 30     int my_begin = -1, my_end = -1;
 31     for (int i = 0; i < 26; ++ i)
 32     {
 33         if (out[i] != in[i])
 34         {
 35             if (out[i] - in[i] == 1 && my_begin == -1) my_begin = i;
 36             else if (out[i] - in[i] == -1 && my_end == -1) my_end = i;
 37             else return -1;
 38         }
 39     }
 40     if (my_begin > -1 && my_end > -1) return my_begin;
 41     if (my_begin == -1 && my_end == -1)
 42     {
 43         for (int i = 0; i < 26; ++ i)
 44             if (out[i] != 0) return i;
 45     }
 46     return -1;
 47 }
 48 
 49 bool dfs(int my_loc_int, int cnt)
 50 {
 51     if (cnt == n) return true;
 52     for (int i = 0; i < n; ++ i)
 53     {
 54         if (my_book[i] || my_str[i].h < my_loc_int) continue;
 55         else if (my_str[i].h > my_loc_int) return false;
 56         else
 57         {
 58             my_book[i] = 1;
 59             my_route[cnt] = i;
 60             if (dfs(my_str[i].t, cnt + 1)) return true;
 61             my_book[i] = 0;
 62         }
 63     }
 64     return false;
 65 }
 66 
 67 int main()
 68 {
 69     ios::sync_with_stdio(false);
 70     int t;
 71     scanf("%d", &t);
 72     while (t --)
 73     {
 74         /**
 75             初始化
 76         */
 77         memset (in, 0, sizeof(in));
 78         memset (out, 0, sizeof(out));
 79         memset (my_book, 0, sizeof(my_book));
 80 
 81         /**
 82             输入数据
 83         */
 84         scanf("%d", &n);
 85         for (int i = 0; i < n; ++ i)
 86         {
 87             scanf("%s", my_str[i].s);
 88             int len = strlen(my_str[i].s);
 89             my_str[i].h = my_str[i].s[0] - ‘a‘;
 90             my_str[i].t = my_str[i].s[len - 1] - ‘a‘;
 91             out[my_str[i].h] ++;
 92             in[my_str[i].t] ++;
 93         }
 94 
 95         /**
 96             @parm: my_begin 开始位置的首字母对应ASC - ‘a‘
 97         */
 98         int my_begin = euler();
 99         if (my_begin == -1)
100         {
101             printf("***\n");
102             continue;
103         }
104         sort(my_str, my_str + n, cmp);
105         /**
106             判断是否能找出这样一条路径来
107         */
108         if (dfs(my_begin, 0))
109         {
110             for (int i = 0; i < n-1; ++ i)
111                 printf("%s.", my_str[my_route[i]].s);
112             printf("%s\n", my_str[my_route[n - 1]].s);
113         }
114         else
115         {
116             printf("***\n");
117         }
118     }
119 
120     return 0;
121 }