Codeforces - 518D 概率DP初步

#include<iostream>

#include<algorithm>

#include<cstdio>

#include<cstring>

#include<cstdlib>

#include<cmath>

#include<string>

#include<vector>

#include<stack>

#include<queue>

#include<set>

#include<map>

#define rep(i,j,k) for(register int i=j;i<=k;i++)

#define rrep(i,j,k) for(register int i=j;i>=k;i--)

#define erep(i,u) for(register int i=head[u];~i;i=nxt[i])

#define iin(a) scanf("%d",&a)

#define lin(a) scanf("%lld",&a)

#define din(a) scanf("%lf",&a)

#define s0(a) scanf("%s",a)

#define s1(a) scanf("%s",a+1)

#define print(a) printf("%lld",(ll)a)

#define enter putchar('\n')

#define blank putchar(' ')

#define println(a) printf("%lld\n",(ll)a)

#define IOS ios::sync_with_stdio(0)

using namespace std;

const int maxn = 2333+11;

const int oo = 0x3f3f3f3f;

const double eps = 1e-7;

typedef long long ll;

ll read(){

    ll x=0,f=1;register char ch=getchar();

    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}

    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}

    return x*f;

}

int n;

double dp[maxn][maxn];

int main(){

	int n,t;double p;

	while(cin>>n>>p>>t){

		dp[0][0]=1;

		rep(i,1,n)dp[0][i]=0;

		rep(i,1,t){

			rep(j,0,n){

				if(j==0) dp[i][0]=(1-p)*dp[i-1][0];

				else if(j==n) dp[i][n]=dp[i-1][n]+p*dp[i-1][n-1];//note

				else dp[i][j]=p*dp[i-1][j-1]+(1-p)*dp[i-1][j];

			}

		}

		double ans=0;

		rep(i,1,n) ans+=dp[t][i]*i;

		printf("%.6lf\n",ans);

	}

	return 0;

}
巴特西

Codeforces - 518D 概率DP初步

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