版权声明:喜欢请点个大拇指,感谢各位dalao。弱弱说下,转载要出处呦 https://blog.csdn.net/qq_35786326/article/details/83113989
题目:
分析:
直接组合数套上,不多说
然后值得一提的是题目超水的数据,连费马小定理都不用就可以
代码:
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<set>
#include<queue>
#include<vector>
#include<map>
#include<list>
#include<ctime>
#include<iomanip>
#include<string>
#include<bitset>
#include<deque>
#include<set>
#define LL long long
#define ch cheap
#define XJQ 100000007
using namespace std;
inline LL read() {
LL d=0,f=1;char s=getchar();
while(s<'0'||s>'9'){if(s=='-')f=-1;s=getchar();}
while(s>='0'&&s<='9'){d=d*10+s-'0';s=getchar();}
return d*f;
}
int x[2005];
int a=read(),b=read();
void fac()
{
x[1]=1;
for(int i=2;i<=a*2;i++)
x[i]=x[i-1]*i%XJQ;
return;
}
int main()
{
fac();
cout<<x[2*a]/(x[b]*x[2*a-b]);
return 0;
}