1827A-CountingOrders.cpp

#include <cstdio>
#include <vector>
#include <algorithm>

int main(){


    long long MOD = 1e9 + 7;
    long t; scanf("%ld", &t);
    while(t--){
        long n; scanf("%ld", &n);
        std::vector<long> a(n), b(n); 
        for(long p = 0; p < n; p++){scanf("%ld", &a[p]);}; sort(a.begin(), a.end());
        for(long p = 0; p < n; p++){scanf("%ld", &b[p]);}; sort(b.begin(), b.end());

        long idx(n - 1); long long res(1);
        for(long p = n - 1; p >= 0; p--){
            while(idx >= 0 && a[idx] > b[p]){--idx;}
            long diff = p - idx;
            if(diff < 0){res = 0; break;}
            res *= diff; res %= MOD;
        }

        printf("%lld\n", res);
    }

}