poj 2151 Check the difficulty of problems (DP)
2012-07-31 20:33
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在acm比赛中,n题,t队。给出每个队做对每题的概率,问每队至少对一题,至少有一队做对至少m题的概率
dp,f[i][j]表示第i个队伍做对第j题的概率。g[i][j][k]表示第i个队伍对于前j题而言做对k道的概率。
g[i][j][k] = g[i][j - 1][k - 1] * (f[i][j]) + g[i][j - 1][k] * (1 - f[i][j]);
有了所有的g,我们就可以求出每个队至少做对1题的概率:ans *= 1 - g[i]
[0];
再减去每个队都只做对1~m-1题的概率(把每个队做对1~m-1题的概率加和,并把各队结果相乘)
#include"stdio.h"
#include"string.h"
double map[1001][31],dp[1001][31][31];
int main()
{
int i,j,k,n,m,t;
double ans,sum,temp;
while(scanf("%d%d%d",&n,&t,&m)!=-1)
{
if(n==0&&m==0&&t==0)break;
for(i=0;i<t;i++)
{
for(j=1;j<=n;j++)
scanf("%lf",&map[i][j]);
}
memset(dp,0,sizeof(dp));
for(i=0;i<t;i++)
{
dp[i][0][0]=1;
for(j=1;j<=n;j++)
{
dp[i][j][0]=dp[i][j-1][0]*(1-map[i][j]);
for(k=1;k<=j;k++)
dp[i][j][k]=dp[i][j-1][k]*(1-map[i][j])
+dp[i][j-1][k-1]*map[i][j];
}
}
ans=1;
for(i=0;i<t;i++)
ans*=1-dp[i]
[0];
temp=1;
for(i=0;i<t;i++)
{
sum=0;
for(j=1;j<m;j++)
{
sum+=dp[i]
[j];
}
temp*=sum;
}
ans-=temp;
printf("%.3f\n",ans);
}
return 0;
}
在acm比赛中,n题,t队。给出每个队做对每题的概率,问每队至少对一题,至少有一队做对至少m题的概率
dp,f[i][j]表示第i个队伍做对第j题的概率。g[i][j][k]表示第i个队伍对于前j题而言做对k道的概率。
g[i][j][k] = g[i][j - 1][k - 1] * (f[i][j]) + g[i][j - 1][k] * (1 - f[i][j]);
有了所有的g,我们就可以求出每个队至少做对1题的概率:ans *= 1 - g[i]
[0];
再减去每个队都只做对1~m-1题的概率(把每个队做对1~m-1题的概率加和,并把各队结果相乘)
#include"stdio.h"
#include"string.h"
double map[1001][31],dp[1001][31][31];
int main()
{
int i,j,k,n,m,t;
double ans,sum,temp;
while(scanf("%d%d%d",&n,&t,&m)!=-1)
{
if(n==0&&m==0&&t==0)break;
for(i=0;i<t;i++)
{
for(j=1;j<=n;j++)
scanf("%lf",&map[i][j]);
}
memset(dp,0,sizeof(dp));
for(i=0;i<t;i++)
{
dp[i][0][0]=1;
for(j=1;j<=n;j++)
{
dp[i][j][0]=dp[i][j-1][0]*(1-map[i][j]);
for(k=1;k<=j;k++)
dp[i][j][k]=dp[i][j-1][k]*(1-map[i][j])
+dp[i][j-1][k-1]*map[i][j];
}
}
ans=1;
for(i=0;i<t;i++)
ans*=1-dp[i]
[0];
temp=1;
for(i=0;i<t;i++)
{
sum=0;
for(j=1;j<m;j++)
{
sum+=dp[i]
[j];
}
temp*=sum;
}
ans-=temp;
printf("%.3f\n",ans);
}
return 0;
}
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