1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 const int MAXN = 66;
 6 int nxt[MAXN];
 7 void GetNxt(char p[], int m)
 8 {
 9     int j = 0, k = -1;
10     nxt[0] = -1;
11     while(j < m)
12     {
13         if(k != -1 && p[j] != p[k]) k = nxt[k];
14         else nxt[++j] = ++k;
15     }
16 }
17 int KMP(char s[], int n, char p[], int m)
18 {
19     int res = 0;
20     for (int i = 0, k = 0; i < n; i++)
21     {
22         while (k > 0 && p[k] != s[i]) k = nxt[k];
23         if (p[k] == s[i]) k++;
24         res = max(res, k);
25         if (k == m) k = nxt[k];
26     }
27     return res;
28 }
29 char p[MAXN], s[20][MAXN];
30 int n, t, len;
31 int ans;
32 char res[MAXN], T[MAXN];
33 int main()
34 {
35     scanf("%d", &t);
36     while (t--)
37     {
38         ans = 0;
39         scanf("%d", &n);
40         scanf("%s", p);
41         len = strlen(p);
42         for (int i = 1; i < n; i++) scanf("%s", s[i]);
43
44         for (int i = 0; i < len; i++) // 枚举每一个后缀
45         {
46             int tmp = 66;
47             GetNxt(p+i, len-i);
48             for (int j = 1; j < n; j++)
49                 tmp = min(tmp, KMP(s[j], len, p+i, len-i)); // 公共匹配的长度
50
51             strncpy(T, p+i, tmp);
52             T[tmp] = '\0';
53             if (tmp > ans) //记录最大值
54             {
55                 ans = tmp;
56                 strcpy(res, T);
57             }
58             else if (tmp == ans && strcmp(res, T) > 0)
59             {
60                 strcpy(res, T);
61             }
62         }
63         if (ans < 3) puts("no significant commonalities");
64         else puts(res);
65     }
66 }