1245 Problem -AL-ACM CLUB party - Getting title - mathematics -C ++ realization

Problem AL: ACM CLUB party

Time limit: 1 Sec Memory Limit: 32 MB
submitted: 140 solved: 31

Title Description

ACM CLUB members more and more, to this end, ACM CLUB would like to prepare a party for members, evening performances by the members. The news came out, a lot of performances to sign up members, up to N, but due to limited space and time, only individuals selected from N M number, how many choices there are a method to ask?

Entry

A first data line T is a positive integer, the next set of data with a T, each data per line.
Each set of data contains two integers N (number of people to sign up, 1 <= N <= 30 ), M ( number of required program 0 <= M <= 30) .

Export

The data output of each group an integer, each output per line.

Sample input  Copy

5
3 2
5 3
4 4
3 6
8 0

Sample output  Copy

3
10
1
0
1

Code

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
using namespace std;
//longlong 在此情况下也有可能会溢出，所以必须选择一个较小值来进行排列组合，进行运算优化
unsigned long long find(int a,int b){
  unsigned long long m=1,n=1;
  for (int i = 1; i <=b; i++)
  {
    m*=a;
    a--;
    n*=i;
  }
 unsigned long long cc=m/n;
  return (cc);
  
}
int main(){
  int num;
  int a,b;
  cin>>num;
  getchar();
  if(num>0){ 
      while(num--){
        cin>>a>>b;
        getchar();
        if(a>=1&&b>=0&&a<=30&&b<=30){
          if(a<b){
            cout<<0;
            if(num!=0){
              cout<<endl;
            }
          }
          else{
            
              if(b==0||a==b){
                cout<<1;
                if(num!=0){
                  cout<<endl;
                }
                continue;
              }

              int temp=b>(a-b)?(a-b):b;
              unsigned long long c=find(a,temp);
              cout<<c;
              if(num!=0){
                  cout<<endl;
              }        
        }
      }
    }
  }
}