CF 518D(Ilya and Escalator-组合数太大,就直接拿去Dp)
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本题我想求组合数C 发现 C(2000,1000)太大。
于是比赛没做出来。。。。
结果居然只是dp!!
很有道理。。。下次注意
#include<cstdio>#include<cstring>#include<cstdlib>#include<algorithm>#include<functional>#include<iostream>#include<cmath>#include<cctype>#include<ctime>using namespace std;#define For(i,n) for(int i=1;i<=n;i++)#define Fork(i,k,n) for(int i=k;i<=n;i++)#define Rep(i,n) for(int i=0;i<n;i++)#define ForD(i,n) for(int i=n;i;i--)#define RepD(i,n) for(int i=n;i>=0;i--)#define Forp(x) for(int p=pre[x];p;p=next[p])#define Forpiter(x) for(int &p=iter[x];p;p=next[p]) #define Lson (x<<1)#define Rson ((x<<1)+1)#define MEM(a) memset(a,0,sizeof(a));#define MEMI(a) memset(a,127,sizeof(a));#define MEMi(a) memset(a,128,sizeof(a));#define INF (2139062143)#define F (100000007)#define MAXN (2000+10)#define eps (1e-7)long long mul(long long a,long long b){return (a*b)%F;}long long add(long long a,long long b){return (a+b)%F;}long long sub(long long a,long long b){return (a-b+(a-b)/F*F+F)%F;}typedef long long ll;int n,t;double p;long double f[MAXN][MAXN]={0}; int main(){//freopen("Escalator.in","r",stdin);//freopen(".out","w",stdout);cin>>n>>p>>t;if (n>=t){cout<<p*t<<endl;return 0;}f[0][0]=1;Rep(i,t+1)Rep(j,min(i,n)+1){if (j==n) f[i+1][j]+=f[i][j];else{f[i+1][j+1]+=f[i][j]*p;f[i+1][j]+=f[i][j]*(1-p);}}double ans=0;Rep(j,n+1) ans+=f[t][j]*min(j,n);printf("%.10lf\n",ans);return 0;}
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