牛客网小白月赛1 B，I

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <string>
#include <queue>
#include <map>
#include <vector>
#include <iomanip>
using namespace std;
const int maxn = 1e3+50;
const int maxm = 1e4+10;
const int inf = 0x3f3f3f3f;
const double epx = 1e-10;
typedef long long ll;
const ll INF = 1e18;
const double pi = acos(-1.0);
int main()
{
    int t,c;
    double a,b;
    cin>>t;
    while(t--)
    {
        cin>>a>>b>>c;
        cout<<setiosflags(ios::fixed)<<setprecision(c)<<(double)pow(a,exp(1))/b<<endl;//控制输出小数点后位数
    }
}

I题  卡特兰数 出栈序列有多少种

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <string>
#include <queue>
#include <map>
#include <vector>
#include <iomanip>
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;
const int maxn = 5e5+50;
const int inf = 0x3f3f3f3f;
const double epx = 1e-10;
const double pi = acos(-1.0);
typedef long long ll;
const ll INF = 1e18;
const ll mod = 998244353;
ll n,f[maxn];
void ff()
{
    f[0]=1;
    for(int i=1;i<=500000;i++)
        f[i]=(i*f[i-1])%mod;
}
ll poww(ll n,ll m)
{
    ll ans = 1;
    while(m > 0)
    {
        if(m & 1)ans = (ans * n) % mod;
        m = m >> 1;
        n = (n * n) % mod;
    }
    return ans;
}
ll cc(ll n,ll m)
{
    ll ans=f[n];
    ans=(ans*poww(f[m],mod-2))%mod;
    ans=(ans*poww(f[n-m],mod-2))%mod;
    return ans;
}
int main()
{
    int t,kase=1;
    cin>>t;
    ff();
    //cout<<cc(6,3)<<endl;
    while(t--)
    {
        cin>>n;
        int m=n-1;
        ll ans1=(cc(2*n,n)-cc(2*n,n+1))%mod;
        ll ans2=(cc(2*m,m)-cc(2*m,m+1))%mod;
        //cout<<ans1<<" "<<ans2<<endl;
        printf("Case #%d: %lld
",kase++,(ans1-ans2+2*mod)%mod);
    }
}