Light oj 1005 - Rooks (找规律)

题目链接：http://www.lightoj.com/volume_showproblem.php?problem=1005

纸上画一下，找了一下规律，Ank*Cnk.

 //#pragma comment(linker, "/STACK:102400000, 102400000")
 #include <algorithm>
 #include <iostream>
 #include <cstdlib>
 #include <cstring>
 #include <cstdio>
 #include <vector>
 #include <cmath>
 #include <ctime>
 #include <list>
 #include <set>
 #include <map>
 using namespace std;
 typedef long long LL;
 typedef pair <int, int> P;
 const int N = 1e5 + ;

 LL Anm(LL n, LL m) {
     LL ans = ;
     for(LL i = n; i >= n - m + ; --i) {
         ans = ans * i;
     }
     return ans;
 }

 int main()
 {
     int t;
     LL n, k;
     scanf("%d", &t);
     for(int ca = ; ca <= t; ++ca) {
         scanf("%lld %lld", &n, &k);
         printf("Case %d: ", ca);
         if(k > n) {
             printf("0\n");
             continue;
         }
         LL ans = Anm(n, k);
         LL temp = ans;
         for(LL i = k; i >= ; --i) {
             temp /= i;
         }
         printf("%lld\n", ans * temp);
     }
     return ;
 }