密码（Password）

#include<cstdio>
#include<cstring>
using namespace std;
int k, cnt;
char G[2][6][5], ans[6];
bool dfs(int col){
    if (col == 5){
        if (++cnt == k){
            ans[col] = '\0';
            printf("%s\n", ans);
            return true;
        }
        return false;
    }

    bool vis[2][26];
    memset(vis, false, sizeof(vis));
    for (int i = 0; i<2; i++)
    for (int j = 0; j<6; j++)
        vis[i][G[i][j][col] - 'A'] = 1;
    for (int i = 0; i<26; i++)
    if (vis[0][i] && vis[1][i]){
        ans[col] = i + 'A';
        if (dfs(col + 1)) return true;
    }

    return false;
}
int main()
{
    /*
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
    */
    int T;
    scanf("%d", &T);
    while (T--){
        scanf("%d", &k);
        for (int i = 0; i<2; i++)
        for (int j = 0; j<6; j++)
            scanf("%s", G[i][j]);

        cnt = 0;
        if (!dfs(0)) puts("NO");
    }
    /*
    fclose(stdin);
    fclose(stdout);
    */
    return 0;
}