刷题记录
3月16日
[ARC145C] Split and Maximize
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#include <bits/stdc++.h>
using namespace std;
#define int long long
//#define low(x) x&-x
#define fastendl putchar('\n')
inline int read(){int x=0;int f=1;char c=getchar();while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}return x*f;}
int n;int ni[2000010],lx[2000010];
const int mod=998244353;inline int mypow(int a,int b)
{int res=1;while(b){if(b&1)res*=a,res%=mod;a*=a,a%=mod;b>>=1; }return res;
}inline void init()
{lx[0]=1;for(int i=1;i<=2000000;i++)lx[i]=lx[i-1]*i%mod;ni[2000000]=mypow(lx[2000000],mod-2)%mod;for(int i=2000000;i>=1;i--)ni[i-1]=ni[i]*i%mod;
}inline int C(int n,int m)
{if(m<0||n<0)return 0; if(n<m)return 0;return lx[n]*ni[n-m]%mod*ni[m]%mod;
}signed main()
{//freopen("ball.in","r",stdin);//freopen("ball.out","w",stdout);ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);init();n=read();cout<<lx[n]*mypow(2,n)%mod*(C(2*n,n)+mod-C(2*n,n-1))%mod;return 0;
}
E - White and Black Balls
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#include <bits/stdc++.h>
using namespace std;
#define int long long
//#define low(x) x&-x
#define fastendl putchar('\n')
inline int read(){int x=0;int f=1;char c=getchar();while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}return x*f;}
int n,m,k;int ni[2000010],lx[2000010];
const int mod=1e9+7;inline int mypow(int a,int b)
{int res=1;while(b){if(b&1)res*=a,res%=mod;a*=a,a%=mod;b>>=1; }return res;
}inline void init()
{lx[0]=1;for(int i=1;i<=2000000;i++)lx[i]=lx[i-1]*i%mod;ni[2000000]=mypow(lx[2000000],mod-2)%mod;for(int i=2000000;i>=1;i--)ni[i-1]=ni[i]*i%mod;
}inline int C(int n,int m)
{if(m<0||n<0)return 0; if(n<m)return 0;return lx[n]*ni[n-m]%mod*ni[m]%mod;
}signed main()
{//freopen("ball.in","r",stdin);//freopen("ball.out","w",stdout);ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);init();n=read(),m=read(),k=read();if(n>m+k){cout<<0;return 0;}cout<<(C(n+m,m)-C(n+m,n-k-1)+mod)%mod; return 0;
}
[SCOI2010]字符串计数
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#include <bits/stdc++.h>
using namespace std;
#define int long long
//#define low(x) x&-x
#define fastendl putchar('\n')
inline int read(){int x=0;int f=1;char c=getchar();while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}return x*f;}
int n,m;int ni[2000010],lx[2000010];
const int mod=20100403;inline int mypow(int a,int b)
{int res=1;while(b){if(b&1)res*=a,res%=mod;a*=a,a%=mod;b>>=1; }return res;
}inline void init()
{lx[0]=1;for(int i=1;i<=2000000;i++)lx[i]=lx[i-1]*i%mod;ni[2000000]=mypow(lx[2000000],mod-2)%mod;for(int i=2000000;i>=1;i--)ni[i-1]=ni[i]*i%mod;
}inline int C(int n,int m)
{if(m<0||n<0)return 0; if(n<m)return 0;return lx[n]*ni[n-m]%mod*ni[m]%mod;
}signed main()
{freopen("string.in","r",stdin);freopen("string.out","w",stdout);ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);init();n=read(),m=read();cout<<(C(n+m,n)+mod-C(m+n,m-1))%mod;return 0;
}
「TJOI2015」概率论
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#include <bits/stdc++.h>
using namespace std;
#define int long long
//#define low(x) x&-x
#define fastendl putchar('\n')
inline int read(){int x=0;int f=1;char c=getchar();while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}return x*f;}
double n,m;signed main()
{//freopen("string.in","r",stdin);//freopen("string.out","w",stdout);ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);cin>>n;printf("%.10lf",n*(n+1)/(2*(2*n-1)));return 0;
}
