XDOJ_1020_DP

Posted 2020-08-14

http://acm.xidian.edu.cn/problem.php?id=1020

 

简单DP，最近刷刷水题。

 

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;

int n,k;
double a[1005],dp[1005][1005];

int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&n,&k);
        for(int i = 1;i <= n;i++)    scanf("%lf",&a[i]);
        dp[1][0] = 1-a[1];
        dp[1][1] = a[1];
        for(int i = 2;i <= n;i++)
        {
            for(int k = 0;k <= n;k++)
            {
                if(k == 0)    dp[i][k] = dp[i-1][k]*(1-a[i]);
                else        dp[i][k] = dp[i-1][k]*(1-a[i])+dp[i-1][k-1]*a[i];
            }
        }
        double ans = 0;
        for(int i = k;i <= n;i++)    ans += dp[n][i];
        printf("%.4f\n",ans);
    }
    return 0;
}