题解报告：hdu 1570 A C

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1570

Problem Description

Are you excited when you see the title "AC" ? If the answer is YES , AC it ;
You must learn these two combination formulas in the school . If you have forgotten it , see the picture.

Now I will give you n and m , and your task is to calculate the answer .

Input

In the first line , there is a integer T indicates the number of test cases.
Then T cases follows in the T lines.
Each case contains a character 'A' or 'C', two integers represent n and m. (1<=n,m<=10)

Output

For each case , if the character is 'A' , calculate A(m,n),and if the character is 'C' , calculate C(m,n).
And print the answer in a single line.

Sample Input

2

A 10 10

C 4 2

Sample Output

3628800

6

解题思路：组合和全排列！（水题~）

AC代码：

 #include<bits/stdc++.h>
 using namespace std;
 int main()
 {
     int T,n,m,sum;
     char ch;
     cin>>T;
     while(T--){
         getchar();//吃掉回车符
         cin>>ch>>n>>m;
         if(m>n)swap(n,m);//保证m比n小
         sum=;//计数
         if(ch=='A')for(int i=m;i>=;i--)sum*=(n-i+);//全排列
         if(ch=='C'){//组合
             if(n-m<m)m=n-m;//取m最小,减少计算
             for(int i=;i<=m;i++)sum=sum*(n-i+)/i;
         }
         cout<<sum<<endl;
     }
     return ;
 }