2020 CCPC Qinhuangdao Solutions

Problem A

Solution:

　　很简单的组合计数公式题，答案是：$\frac{\binom{r}{2}}{\binom{r+b}{2}}$。

 1 #include "bits/stdc++.h"
 2 #define rep(i,a,n) for(int i=a;i<=n;i++)
 3 #define per(i,a,n) for(int i=n;i>=a;i--)
 4 #define pb push_back
 5 #define mp make_pair
 6 #define FI first
 7 #define SE second
 8 #define maxn 100000
 9 #define mod 1000000007
10 #define inf 0x3f3f3f3f
11 using namespace std;
12 typedef long long ll;
13 typedef pair<int,int> pii;
14 typedef vector<int> vi;
15 typedef double db;
16 
17 int main()
18 {
19     int CAS; scanf("%d",&CAS); rep(cas,1,CAS)
20     {
21         int r,b; scanf("%d%d",&r,&b);
22         int p=r*(r-1)/2,q=(r+b)*(r+b-1)/2;
23         int g=__gcd(p,q);
24         printf("Case #%d: %d/%d\n",cas,p/g,q/g);
25     }
26     return 0;
27 }

View Code