递归一遍遍历所有情况就ｏｋ了
#include<cstdio>
#include<cstring>
#define REP(i, a, b) for(int i = (a); i < (b); i++)
using namespace std;const int MAXN = 10;
char map[2][10][10], str[10];
int k, num;bool dfs(int pos)
{if(pos == 5) return ++num == k;bool vis[2][26];memset(vis, 0, sizeof(vis));REP(i, 0, 2)REP(j, 0, 6)vis[i][map[i][j][pos] - 'A'] = true;REP(i, 0, 26)if(vis[0][i] && vis[1][i]){str[pos] = 'A' + i;if(dfs(pos + 1)) return true;}return false;
}int main()
{int T;scanf("%d", &T);while(T--){scanf("%d", &k);REP(i, 0, 2)REP(j, 0, 6) scanf("%s", map[i][j]);num = 0;if(dfs(0)) puts(str);else puts("NO");} return 0;
}