1023.cpp

#include <bits/stdc++.h>
using namespace std;
vector<char> v;
char arr[] = {"ABCDEFGHIJKLMNOPQRSTUVWXYZ"};
int n, k = 0, ct = 0;
int visit[30] = {0};
void check(void) {
    if (ct == k) return;
    if (v.size() == n) {
        for (int i = 0; i < n; i++) {
            printf("%c", v[i]);
        }
        printf("\n");
        ct++;
        return;
    }
    for (int i = 0; i < n; i++) {
        if (visit[i] == 0) {
            visit[i] = 1;
            v.push_back(arr[i]);
            check();
            v.pop_back();
            visit[i] = 0;
        }
    }
}

int main() {
    int i = 0, t;
    scanf("%d", &t);
    while (t--) {
        i++;
        ct = 0;
        scanf("%d %d", &n, &k);
        printf("Case %d:\n", i);
        check();
    }
    return 0;
}